It should, however, be observed that not all the full-sized seedlings

float. With Rhizophora mangle about 5 per cent. sink in sea-water and

from 20 to 50 per cent. sink in fresh-water; whilst with R. mucronata

the proportion of non-buoyant seedlings is rather greater. There would

thus appear to be a rather nice adjustment of the specific weight of the

seedlings to the density of sea-water. Generally speaking, they may be

seen floating vertically or steeply inclined in the fresh-water of

estuaries and horizontally in the sea. With the buoyant seedlings of

Rhizophora mucronata, as a rule, about 90 per cent. float horizontally

in sea-water, and about 70 per cent. float vertically or steeply

inclined in fresh-water. The same general rule applies to R. mangle,

whether in the rivers and seas of Fiji or in those of Ecuador. In those

cases where the seedling drops prematurely on account either of storms

and floods or of the depredations of a grub that frequently attacks the

fruit, this rule would not apply. One may frequently notice in Fiji

after heavy weather that seedlings detached prematurely, and often

carrying the fruit, are floating in numbers horizontally in the rivers.

In a few days, as a rule, the fruit-case becomes detached and sinks.

It may be remarked that the horizontal position is much better adapted

for the safety of the seedling in transport than the vertical position.

In the last case the plumule, which protrudes above the water, would be

unable, as indicated in my experiments, to withstand the scorching rays

of the sun in a smooth sea; whereas in the horizontal position, which

the seedlings assume in sea-water, the plumule is more or less

completely submerged, and the risk of withering in the sun is very much

less. The Rhizophora seedlings would certainly have little chance of

crossing in safety a large tract of sea, if they floated, as they do in

river-water, with the plumule exposed above the surface. It is not

unlikely that the comparatively restricted area occupied by Rhizophora

conjugata may be due to the attitude its seedlings assume when floating

in sea-water.

The stranded seedlings of Rhizophora readily establish themselves for a

while in very different situations; and it is by no means necessary that

they should be washed ashore on a muddy coast. When half-buried amongst

the heap of vegetable drift piled up on a sandy beach they are

frequently to be found striking into the sand and showing their first

leaves. Here they ultimately perish in the great majority of cases; but

when protected long enough to reach the moist sand four or five inches

below, they may give rise to a little mangrove colony. When caught in a

fissure in the bare reef-flats these plantlets are sometimes able to

establish themselves. Rhizophora seedlings would, however, require a

coast prepared by them by the work of ages before they could form

extensive swamps. It is, therefore, not surprising that Prof. Penzig

found no evidence of mangrove-settlements on the shores of Krakatoa

fourteen years after the eruption.

Yet suited as Rhizophora seedlings are for crossing tracts of sea, I

regard them as quite unfitted for being transported by the currents

unharmed across an ocean. The plumular bud is insufficiently protected

for such a long voyage of many months, and perhaps of years. Though the

horizontal position of the seedling would secure the plumule against

being scorched in the sun, it increases considerably the risk of injury

from direct impact.

As bearing on their capacity for dispersal in other fashions, it may be

remarked that Rhizophora seedlings can withstand long drying. Five which

had been kept dry for nine weeks, after having been found stranded on a

beach, were planted in the mud of a mangrove-swamp. In a fortnight two

of them were developing the first leaves and throwing out roots. As long

as they are protected by a covering of vegetable _débris_ and sand, the

stranded seedlings might retain their vitality for months.

BRUGUIERA RHEEDII (Blume)

This species is reduced in Hooker’s _Flora of British India_ to

Bruguiera gymnorhiza (Lam.), and thus viewed it has a very wide range in

the Old World, corresponding very much to that of Rhizophora mucronata,

namely, tropical East Africa, tropical East Asia to the Liukiu Islands,

the Indian Archipelago, New Guinea, tropical Australia, and Western

Polynesia, as in New Caledonia, Fiji, Tonga, and Samoa. There are four

or five species of the genus, but all are confined to the Eastern

Hemisphere, none occurring in America.

As with the species of Rhizophora, this plant is indebted for its

present dispersal to the floating seedling, which, however, often falls

from the tree whilst still attached to the fruit, but is generally freed

in a day or two. The seedlings float for a long time in sea-water. I

kept one of them afloat for 117 days, when it was quite sound and

healthy. They appear to be better fitted than the species of Rhizophora

for the “rough-and-tumble” of ocean transport, since the plumule is much

less prominent, projecting only one line (2·5 mm.) or less, whilst with

the two Fijian species of Rhizophora the plumule measures from seven to

twelve lines (18 to 30 mm.). In the latter part of the year they are to

be found in abundance in the floating drift of rivers, and there they

readily develop the first leaves and roots. They are also frequent in

the sea off the coasts, and they are stranded in large numbers on the

beaches, where they readily strike into the sand when partially buried

amongst the vegetable drift.

The empty flowers and the germinated fruits containing the cotyledons

are very common in floating drift. They look much alike, but the flowers

are much smaller and possess the long style, whilst the fruits contain

the cotyledons at the bottom of the seed-cavity.

As with Rhizophora, there is a rather curious adjustment of the buoyancy

of the seedling to the density of sea-water. About 75 per cent. of those

afloat in the fresh-water of rivers assume the vertical position, the

plumular end protruding between two and five lines (5 to 12 mm.) above

the surface, while the remainder float horizontally or nearly so. In

sea-water about 50 per cent. float either vertically or steeply

inclined, and the other half float horizontally.

With regard to the times of flowering and fruiting, it may be remarked

that the trees are mostly in flower during the hot months from November

to February, and that the fruiting is in active operation in the latter

half of March. The floating seedlings occur in abundance in the

river-drift at the end of the year, a circumstance which corresponds

with the fact that a period of six months passes between the

fertilisation of the ovule and the fall of the seedling into the water.

Fertilisation, or, more correctly speaking, the discharge of the pollen,

takes place after the opening of the flower, and not before, as in the

case of the species of Rhizophora. The flower-bud is at first erect, but

subsequently it begins to bend downwards, and ultimately it hangs more

or less vertically. The provision to secure fertilisation under these

circumstances is rather curious. Without some such contrivance as is

below described, the pollen would merely fall out of the flower. Each

petal has its sides rolled or folded inwards so as to completely inclose

two stamens. In the bud the folded petals are white and flexible, but as

the flower expands they redden and become dry and elastic, and are only

prevented from flying open with a spring by the interlocking of the

hairy tips of their lobes. Whilst the folded petals are becoming stiff

and elastic during the opening of the flower, the inclosed stamens are

at the same time preparing themselves for their function. The anthers

are dehiscing and the filaments are acquiring elasticity. All is now

ready, and a slight shake or a touch puts the mechanism into action. The

petals unfold themselves with a spring, and the stamens thus suddenly

exposed and released fly forward, and a little shower of pollen is

thrown towards the centre of the flower. This process is accomplished in

ordinary fine weather during the first twenty-four or thirty-six hours

after the expansion of the flower. When the opening occurs in the early

morning, half of the stamens will be found released in the evening and

the rest on the following day. During the next day or two the petals and

the stamens fall out of the flower. In wet weather, the petals never

acquire elasticity, and in consequence do not unfold. In this case

pollenisation is never effected, and the folded petals soon fall to the

ground, carrying the stamens within them. Cross-fertilisation would be

much more likely to occur with species of Bruguiera (if, as is probable,

the same process of pollenisation is usually followed) than with species

of Rhizophora, since the stamens are securely inclosed in the petals for

some hours after the expansion of the flower.

Nearly eight weeks pass between the date of fertilisation and the

commencement of germination. This is somewhat similar to the period

given for Rhizophora mangle, namely, nine weeks, and it obviously leaves

little or no time for any stage of quiescence or dormant vitality in the

case of the seed. The changes which the fruit undergoes in this interval

are a considerable increase in girth and a thickening of the calycine

walls, together with a contraction of the mouth of the tube. However, I

found no method sufficiently accurate for recording the rate of increase

of the fruit.

It is known that germination is in progress when the end of the

hypocotyl begins to lift up the lining membrane at the bottom of the

calycine tube (see Figs. 21 to 26). The floor of the tube begins to

bulge up, but since this cannot be well seen at first, a better index is

afforded in the elevation of the style which accompanies it. The top of

the style preserves previous to this time a constant level with regard

to the tips of the calycine teeth. But this does not indicate the actual

beginning of germination. As shown in Fig. 21, the seed lies about two

and a half lines (6 mm.) below the floor of the calycine tube, and the

tip of the hypocotyl has to penetrate the intervening tissues before it

can push up the lining membrane and raise the style. Judging from the

subsequent rate of growth, seven or eight days at least, and perhaps as

much as two weeks, are requisite for this purpose. It is not necessary

to give further details here, and it may be at once stated that the

average of numerous observations on the length of the interval between

fertilisation and the elevation of the style was sixty-four days, the

range being fifty-nine to sixty-nine. After deducting ten days for the

time occupied for the radicle in reaching the floor of the calycine tube

(see Figs. 22 and 23), we obtain, as already remarked, nearly eight

weeks as the time elapsing between fertilisation and germination.

The radicle or hypocotyl, therefore, in the first stage of germination

pierces the tissues above it and reaches the floor of the calycine tube.

It does not, however, pierce the lining membrane of the tube but pushes

it upward until it ruptures about 4 millimetres below the base of the

style which is carried up with it. Thus a kind of cap is formed, as

shown in Fig. 24, which does not fall off from the end of the hypocotyl

until it has protruded rather more than an inch. The hypocotyl attains a

length varying between 5 and 11 inches, the average being about 8

inches.

The whole period may be thus divided up:—

(1) Period between fertilisation and germination 7-1/2

weeks.

(2) Period between the beginning of germination and the 1-1/2

protrusion of the point of the hypocotyl at the floor of the weeks.

calycine tube

(3) Period occupied in the growth of the hypocotyl 8 inches 18 weeks.

outside the fruit and terminating in the fall of the

seedling

——

Total 27 weeks.

The total period of twenty-seven weeks between fertilisation and the

fall of the seedling is thus six weeks shorter than that estimated for

Rhizophora mangle. On comparing the two tables it will be seen that the

difference mainly lies in the length of the second period, namely, that

between the commencement of germination and the protrusion of the

hypocotyl from the fruit. With Rhizophora mangle the fruit grows

considerably in length during this period of the germinating process. On

the other hand with Bruguiera rheedii there is, during this period,

practically no increase in the length of the fruit, and the radicle has

only to penetrate the tissues, 2-1/2 lines in thickness, between the

seed and the floor of the calycine tube.

In the mode of separation of the seedling there are very marked

differences between this species of Bruguiera and the species of

Rhizophora. With Bruguiera rheedii the four small cotyledons, which are

united at the base, are, however, left behind at the bottom of the

seed-cavity, when the seedling is detached. But there is no expulsion of

the seedling, the connection being ultimately severed at the contracted

base of the cotyledons inside the fruit. When the seedling is full-sized

the nutritive supply begins to fail, and in consequence the pressure of

the sides of the fruit on the inclosed plumular end of the seedling

becomes slacker, the union with the cotyledons becomes weaker, and the

connection of the fruit with its peduncle at the basal joint becomes

slighter. Usually the fruit falls before the seedling is ready to drop

out, and the connection is severed after a few days’ flotation in the

water; but sometimes the union between the seedling and fruit is weaker

than that between the fruit and its peduncle, and in that case the

seedling falls and leaves the fruit containing the cotyledons on the

tree. The whole process of separation is much simpler than with species

of Rhizophora. Here it is mainly a matter of the failure of the

nutritive supply, whilst with Rhizophora it is almost a process of

parturition.

Haberlandt, in the memoir before quoted, describes quite a different

mode of detachment in the case of Bruguiera eriopetala. Here the

seedling falls normally whilst still attached to the fruit, and the

separation is subsequently effected by the expansion of the mouth of the

calyx-tube due to the swelling of the “endosperm-neck” from the entrance

of water.

_Summary_

(1) There are four typical mangroves of the Rhizophoraceæ in Fiji,

Bruguiera rheedii, Rhizophora mucronata (the Asiatic species),

Rhizophora mangle (the American species), and the Selala, a seedless

form intermediate between the two species of Rhizophora just named, but

nearest to the Asiatic species.

(2) It is shown that the sterility of the Selala is connected with the

impotent character of the pollen; and since the ovules appear capable of

fertilisation this is held to indicate that cross fertilisation has not

been in operation in producing the barren form.

(3) Good reasons are given for the belief that the Asiatic species of

Rhizophora is the parent of the Selala, not as the result of a cross

between the Asiatic and American species, but as connected with

dimorphism, the Asiatic species producing two kinds of offspring, one of

them with impotent pollen.

(4) In support of this view it is pointed out that there are two forms

of Rhizophora mangle in Ecuador, one of which comes near the Fijian

Selala, though producing seed. There could thus be no question of

crossing, since but one species occurs there.

(5) The Selala reproduces itself in a vegetative fashion when growing,

as it often does, in an inclined position. The parent trunk dies and the

primary branches supported by the aërial roots, remain alive and in

their turn give rise to secondary branches similarly supported.

(6) Although, as a rule, only one of the four ovules of Rhizophora

becomes a seed, occasionally a fruit contains more than one seed. With

R. mangle in Fiji about one per cent. of the germinating fruits

displayed more than one hypocotyl.

(7) As a result of a protracted series of observations in Fiji, it was

established that in the case of a seedling of average length of

Rhizophora mangle a period of thirty-three weeks elapsed between the

date of fertilisation of the ovule and the detachment of the seedling

from the tree. In the instance of R. mucronata it was placed at

forty-two weeks. A period of thirty-eight weeks, or nine to ten months,

is regarded as typical for the genus.

(8) It is established that normally there is no rest-period for the seed

in the case of Rhizophora, the seed at once beginning to germinate on

reaching maturity. In those exceptional instances, however, where there

is more than one seed, it is shown that in some cases the seeds do not

begin to germinate together, and that a rest-period of at least some

weeks can be at times postulated for one of the seeds.

(9) An analogy exists between the process of expulsion ending in the

detachment of the seedling of Rhizophora from the fruit and the process

of parturition.

(10) Experiments show that Rhizophora seedlings can float unharmed in

sea-water for a period of at least three or four months. Though

nine-tenths or more float in sea-water, as much as a fourth or a half

sink in fresh-water. As a rule they float vertically in fresh-water and

horizontally in sea-water, the horizontal position safe-guarding the

plumule against the risk of being withered up by the sun in a calm sea.

(11) It is shown that in the case of Bruguiera rheedii the seedlings

when detached from the tree can float unharmed in sea-water for months.

In their specific weight they display a similar fine adjustment to the

density of sea-water, as is above described in the case of Rhizophora.

(12) With this species of Bruguiera, fertilisation takes place not in

the unopened flower, as in Rhizophora, but after the flower’s expansion;

and a very singular mechanism is here described which secures the

completion of the process.

(13) A period of twenty-seven weeks elapses between the fecundation of

the ovule and the detachment of the seedling from the tree in the case

of Bruguiera rheedii; and it is shown that there is normally little or

no room for any rest-period, and that, as with Rhizophora, the seed on

reaching maturity begins to germinate.

(14) Though the seedlings of Rhizophora and Bruguiera could be

transported in safety a few hundred miles across the sea, it is held

that they could never cross the Pacific and reproduce the plant. That

the American species of Rhizophora has reached the Western Pacific from

the New World is not accepted. Rather is its present distribution

regarded as representing its original wide range over much of the

tropical zone.

CHAPTER XXXI

A CHAPTER ON VIVIPARY

The significance of vivipary.—The scale of germinative capacity.—A lost

habit with many inland plants.—The views of Goebel.—The shrinking in

the course of ages of tropical swamp areas.—The variation in the

structures concerned with vivipary.—Abnormal vivipary.—Summary.

IT was remarked in Chapter IX that the study of the germination of the

floating seed carried us to the borderland of vivipary; and we may now

observe that our study of the mangroves, Rhizophora and Bruguiera, in

the previous chapter, has brought us into contact with vivipary in its

most complete development in the tropical swamps of our age. There is a

great gap between the two extremes, represented by the occasional

germination of a seed in a capsule or in a berry on the plant, and by

the elaborate process of vivipary exemplified by Rhizophora; but most of

the intermediate stages can be illustrated by known examples of

vivipary. There is, however, no pretension to deal with this subject

here in anything but a cursory fashion; but it will, I venture to think,

add completeness to a work in which germination on and off the plant has

been such a frequent theme if I endeavour to connect together some of

the various sets of facts known to us concerning germination from the

standpoint of vivipary.

The principal argument here followed has been already outlined in

Chapter IX, where I have remarked that it is possible to construct a

scale of the germinative capacities of plants, presenting a continuous

series beginning with the mangroves, where germination takes place on

the tree, and ending with those numerous inland plants where seeds are

liberated in an immature condition. It is suggested that vivipary was

the rule under the uniform climatic conditions of early geological

periods, and that with the differentiation of climates that has marked

the emergence of the continents the viviparous habit has been lost over

much of the globe, the mangrove-swamps alone illustrating the climatic

conditions once prevailing. The rest-period of the seed is regarded as

an adaptation to climatic differentiation and to seasonal variation; and

even the seed-stage may be broadly regarded as the price paid for

adaptation on the part of the evolutionary or determining power that

lies behind plant-development. When discussing the germination of

Cæsalpinia in Chapter XVII, I have shown that the contraction and

induration of the seed-tests appear merely as an adaptation to climatic

differentiation and to seasonal variation, and that it would be quite

possible by exposing the maturing seed to very warm and moist conditions

to induce germination without any rest-period, as actually occurs with

Rhizophora. One would then dispense altogether with the final processes

of the contraction and induration of the seed-coats, as illustrated in

the Leguminosæ; and the rest-stage would appear as an adaptation to

secular differentiation of climate in the later epochs of the world’s

history.

The significance of occasional vivipary was long ago pointed out by

Goebel in his _Pflanzenbiologische Schilderungen_ (teil I., 117-134,

Marburg, 1889), when he observed that vivipary, as displayed in the

mangroves, and particularly in the Rhizophoreæ, represented the fullest

expression of a habit that is only occasionally exhibited by other

plants under exceptionally moist conditions. His view was that the seeds

of plants living in wet places are suited in a varying degree for rapid

germination, and that vivipary presents itself as the most complete

development of this capacity. If I regard the views of Goebel and of

Kerner aright, vivipary as normally developed in the mangrove is to be

traced in a descending scale to small beginnings, the principal

determining condition lying in the great difference that exists amongst

plants in the readiness of the seed to germinate. In the ascending scale

we would have first the detachment of the immature seed, where the

embryo is often in a rudimentary state, the ripening of the seed taking

place in the soil. Then would come those plants where the seeds on being

detached are quite mature and are ready to germinate as soon as they

fall to the ground. Then would follow the stage represented by those

plants where the seeds merely begin to germinate on the plant, such as

occurs more or less normally with some mangroves like Laguncularia, and

abnormally with a number of plants living in drier stations. After this

come those mangroves, where, as in Avicennia, germination is completed

on the tree or shrub, but the seedling at once liberates itself from the

parent. Last of all there is the stage of the typical mangroves,

Rhizophora and Bruguiera, where the seedling remains for months growing

on the tree and hangs from the branches.

Vivipary, as above stated, presents itself as a matter of small

beginnings. My own view, however, is that it is a matter of small

“endings”; and that if we were to commence the scale not with the

immature seed lying on the soil, but with the seedling suspended from

the branches of a Rhizophora tree, we should record the various epochs

in the history of vivipary throughout the plant-world. From this

standpoint the occasional cases of incomplete vivipary displayed outside

the mangrove-swamp represent a lost habit belonging to a primeval period

when the climatic conditions were uniform over most of the earth, an age

almost of eternal gloom, when the air was ever saturated with aqueous

vapour, and when the sun’s rays were screened off by a dense

cloud-covering that enveloped the globe, an age of which the existing

mangrove swamps alone afford an imperfect indication. Yet even now we

can say with Schimper that “dense and frequently repeated cloudiness

apparently represents the most essential climatic condition for the

occurrence of mangrove in the tropics” (_Plant Geography_, p. 409).

But, to return to the subject immediately under consideration, if my

view is correct we ought to find indications of the lost habit in the

anomalous structure of the seeds of some inland plants; and, indeed, it

is shown in Note 50 that this view can be taken of the singular

structure of the seeds of the Myrtaceous genera, Barringtonia and

Careya, and of the genera of some other orders, and can be extended by

implication to several other plants possessing similar seed-structures.

With regard to the subject generally, it may be remarked that although

normal vivipary is mainly restricted to the plants of a mangrove swamp,

by no means all mangrove plants are typically viviparous. This habit in

its most complex form is exhibited as a rule by plants with firm,

somewhat fleshy, usually one-seeded, indehiscent fruits, such as we find

with Rhizophora and Bruguiera; but plants with follicular fruits, such

as occur with Ægiceras, may also display it in a fashion nearly as

complex. Generally speaking, however, plants with hard, dry fruits, such

as are owned by Excæcaria, Heritiera, and Lumnitzera, are

non-viviparous, though to all appearances quite at home in a

mangrove-swamp. Others again, like Carapa, Laguncularia, and Nipa,

whilst displaying vivipary in a varying degree, in some cases as a

general rule, in others only occasionally, exhibit no special structures

connected with it. This point is well brought out by Schimper in his

work on the Indo-Malayan strand-flora (p. 43), and no further mention

need be made of it here.

The structures connected with vivipary vary greatly in their degree of

specialisation. At the one end of the scale we have highly complex

structures, such as are described in the preceding chapter. At the other

end we have those cases of occasional germination on the parent plant

where there is seemingly no special structure of any sort. That the

complex arrangements concerned with the vivipary of Rhizophora,

Bruguiera, Ægiceras, and Avicennia are adaptations is argued by

Haberlandt and Schimper, both of whom devoted much attention to the

study of these plants. This is seemingly indicated by the circumstance

that complex structures concerned with vivipary are found in plants so

divergent in their characters (the four genera above-named representing

three orders, Rhizophoreæ, Myrsinaceæ, and Verbenaceæ) that they only

possess their stations in common. It does not, however, follow that all

mangroves that exhibit a complex form of vivipary are of the same

antiquity. I should be inclined to regard those of the Rhizophoreæ as

the more primitive types, whilst it is possible that plants of other

orders, though ancient denizens of a mangrove-swamp, may be more recent

intruders into the mangrove-formation after the differentiation of a

dry-land flora.

Of particular interest in this connection are the cases of abnormal

vivipary, or of “precocious germination,” that have been recorded from

time to time respecting a number of plants not denizens of a mangrove

swamp, none of which would appear, according to Schimper’s views, to

present anything of the nature of an adaptation. Goebel mentions a

number of instances, such as that of wheat-grains germinating on the

stalk in a wet summer, and that of Dryobalanops camphora, the Borneo

camphor-tree, when during a prolonged wet season in Java the seed

germinates in the fruit on the parent tree. Amongst other examples he

cites the Cacti, Epilobium, Agrostemma, and Juncus, the last case coming

also under my observation in a wet season in England. One may here

notice the instance of Dracæna, of which Mr. Hemsley, in April, 1902,

exhibited at a meeting of the Linnean Society of London a specimen

showing the seeds germinating in the berries on the plant.

Several cases of this kind came under my notice in Fiji. Pulpy fruits

rather favour the precocious germination of seeds. Thus I sometimes

found the seeds germinating in the Mandarin orange and in the Papaw

fruit (Papaya) shortly after they had been gathered. But more

interesting examples were displayed in those instances where the seed

was found germinating on the plant. When the Convolvulaceæ grew in wet

situations, as on the borders of a mangrove swamp, the seeds were

sometimes observed germinating in the capsule. This came under my notice

with Ipomœa glaberrima (Boj.) and with I. peltata, more particularly in

wet weather. With some other plants, like Hibiscus diversifolius, that

grow in wet places, this at times occurs. A species of Croton, employed

as a support for the Vanilla plants in a plantation near Suva, displayed

seeds germinating on the plant. I was informed that the seeds of the

common cultivated Luffa (L. cylindrica) growing in a garden on Vanua

Levu sometimes germinated in the fruit still attached to the parent. It

is possible that the seeds of the parasitical genus, Myrmecodia, may

occasionally germinate on the plant, since I found them germinating

inside some of the small berries that had been lying forgotten within a

newspaper for a fortnight.

Perhaps the most curious case of abnormal vivipary observed by me in

Fiji was that concerned with the Coco-nut palm. Though not known to many

residents in the island, this habit was described to me by Mr. Matthew

Simpson, a planter on Vanua Levu, who told me that he had noticed nuts

germinating on the tree in unusually dry seasons. Coco-nut palms

displaying the nuts germinating on the tree came under my observation

near Bale-bale, Savu-Savu Bay. In these cases the mature fruit, instead

of falling, remains attached and dries on the stalk. In one case the

seedling was about eighteen inches high. This seems to be what takes

place normally according to Blume with Nipa fruticans, the swamp palm of

Indo-Malaya. Goebel quotes this author to the effect that the fruits are

not separated from the head before germination is so far advanced that

sea-water can no longer injure the seedling. The fruits, we are told,

may remain for years attached in a state of incomplete germination.

_Summary_

The scale of germinative capacity, that begins with the seedling hanging

from the branches of a mangrove like Rhizophora and ends with the

detached immature seeds of many inland plants that only germinate after

lying for some time in the soil, is regarded as supplying a record of

the various epochs in the history of vivipary throughout the

plant-world. In the occasional cases of incomplete vivipary occurring

among inland plants and in the singular structure presented by the seeds

of certain genera of the Myrtaceæ and other orders we perceive

indications of a lost viviparous habit belonging to a primeval period

when vivipary was the exception and not the rule, an age when the same

climatic conditions prevailed over much of the globe. At such a period

the sun’s rays were screened off by a dense cloud-covering that

enveloped the earth, and the atmosphere was ever charged with moisture.

With the differentiation of climate that has marked the emergence of the

continents during the secular drying of the earth, the viviparous habit

has been alone retained within the confines of the mangrove-swamp, where

the conditions once almost universal now survive; and as an adaptation

to the differentiation of climate and to the resulting seasonal

variation the rest-period of the seed has been developed.

CHAPTER XXXII

THE WEST COAST OF SOUTH AMERICA

The littoral floras of the West Coast of South America.—The Convolvulus

soldanella zone of Southern Chile.—The plantless or desert zone of

Northern Chile.—The Sesuvium zone of Peru.—The Mangrove zone of

Ecuador and Colombia.—The two varieties of Rhizophora mangle, the

“mangle chico” and the “mangle grande.”—The floating vegetable drift

of the Guayaquil River.—The Humboldt current and the climate of the

West Coast of South America.—The advance northward of the arid

climatic conditions of the Peruvian sea-border.—The retreat of the

mangroves.—Evidence of ancient coral reefs on the coast of Peru.—The

shore plants and stranded seed-drift of the Panama Isthmus.—Summary.

MY acquaintance with the strand-flora of the west coast of South America

began at Corral, the port of Valdivia, in Southern Chile in lat. 40° S.,

and terminated at the mouth of the Guayaquil River, in Ecuador, about 2°

south of the equator. During the period December 23, 1903, to March 17,

1904, I examined the coast plants at sixteen localities in this region,

which covers 38 degrees of latitude and thus measures about 2,300 miles.

Travelling in a steamer to Callao that was trading on the coast I had

opportunities of staying for periods ranging from half a day to a couple

of days at a considerable number of places; and a week spent at

Valparaiso gave me a good opportunity of examining the beaches north and

south of it. At Lima I spent some weeks, and from that centre examined

the shore-plants at Callao, Ancon, and Chancay to the northward. North

of this I had not the same opportunities, until we passed the Peruvian

and Ecuadorian boundary; but from a visit to the shore at Paita, from

the general look of the country in places as we coasted along, and from

information derived from other sources, I was able to obtain a fair

general idea of the prevailing character of the beach plants. After my

previous experience to the southward, one could fairly gauge the

character of the beach-flora from the appearance of the land behind. In

the Gulf of Guayaquil and in the vicinity of the city of that name I

spent about three weeks in the investigation of the coast flora.

If it were not for the interposition of the great rainless deserts of

Northern Chile and for the scantily vegetated, scantily watered and

semi-sterile condition of almost the whole coast of Peru, the botanist

would be presented with a splendid opportunity of studying the

distribution of shore-plants along a meridian stretching through some

fifty degrees of latitude from Patagonia to Ecuador. As it is, drought

and sterility in one form and another reign over about half of this

great stretch of continental coast. This is reflected in the

beach-flora; and though the observer will often have his interest

attracted by the wonderful climatic anomalies arising from the presence

on the coast of the cold Humboldt current, to which the sea-border of

North Chile owes its desolation and the coast of Peru its

semi-sterility, yet for a long time he will feel as if Nature had hardly

dealt fairly with him.

[Illustration:

THE WEST COAST

OF

SOUTH AMERICA

John Bartholomew & Co., Edin^r.

]

Along the sea-border corresponding to the deserts of North Chile there

would seem to be practically no plants growing on the beaches, except

here and there where some stray plant from the saline districts inland

intrudes on the coast. Along the whole sea-border of Peru from Arica

north to Tumbez on the borders of Ecuador, the coast-districts, though

more or less rainless, receive the benefit of the drizzly garuas and

sea-fogs, and the sterility of the land immediately backing the beaches

is much less pronounced than with the sea-border corresponding to the

deserts of Northern Chile. This difference shows itself in a peculiar

type of littoral vegetation, a strand-flora that is very scanty but one

where on the beaches Sesuvium prevails. North of Tumbez the

mangrove-formation predominates along the sea-borders of Ecuador and

Colombia to Panama, excepting on a stretch of sterile coast extending

north from the Gulf of Guayaquil to the equator.

Though in one sense the botanical observer will be disappointed with the

littoral floras of the west coast of South America, in another sense

when he remarks the manner in which the coast-vegetation reflects the

abrupt changes in the prevailing climatic conditions he will be

fascinated by the interesting problems presented to him. We are

accustomed to connect a tropical coast with mangroves, coral-reefs, and

beaches of calcareous sand supporting a luxuriant littoral flora.

Climatic conditions banish all these from the tropical west coast of

South America until within four degrees of the equator, and then with

startling suddenness the dominion of the mangrove begins, the

neighbouring hills commence to be clothed with tropical jungle, and the

climate is completely changed. Mr. John Ball, who sailed along this

coast about twenty years ago, referring to this remarkable phenomenon on

the borders of Peru and Ecuador, remarks that no such abrupt and

complete change both in climate and vegetation is known elsewhere in the

world, and he adds that few parts of the American coast better deserve

careful examination (_Naturalist in South America_). This subject has

since been discussed at length by Dr. Wolff in his “Geografia y

Geologica del Ecuador,” and by Baron von Eggers in a paper to be

subsequently quoted, two very competent observers, but the latter

considers that the subject still requires a systematic investigation,

and suggests that an observing station should be established on this

coast by the combined meteorological societies of Europe. A sojourn of

more than a week in the swamps at Puerto Bolivar, a few miles from

Tumbez, enables me to appreciate the nature of the problem, and to throw

a little light on the line of investigation required.

But to return to the general subject of the littoral floras of the west

coast of South America, I may say that beginning with the island of

Chiloe in lat. 42° S., this coast may be divided into four zones.

(1) The Convolvulus soldanella zone of Southern Chile, which extends as

far north as Coquimbo about 30° S. lat.

(2) The Plantless or Desert zone stretching north to the vicinity of

Arica in lat. 18° 30ʹ, and corresponding to the coast of Northern Chile.

(3) The Sesuvium zone, extending north from Arica to the 4th parallel of

south latitude in the vicinity of Tumbez, a sea-border of semi-sterility

that comprises the entire coast of Peru.

(4) The Mangrove zone, stretching from Tumbez, on the frontiers of

Ecuador, to the equator and on to Central America, but interrupted at

first by a strip of sterility on the coast extending from the Gulf of

Guayaquil to the borders of Colombia, or, strictly speaking, to the

equator.

THE CONVOLVULUS SOLDANELLA ZONE (SOUTHERN CHILE).

This zone, which answers to the coast of Southern Chile, from Chiloe as

far north as Coquimbo, corresponds to watered and vegetated inland

regions, in which, however, the amount of rain and the degree of

fertility decreases from south to north, that is to say, as we approach

the desert regions. Here we find none of the dry beaches that prevail

for twenty-five degrees of latitude north of Coquimbo. When we scoop

with our hands to a depth of three or four inches in the sand we find it

relatively cool and more or less moist, as in an English beach. In a hot

summer’s day on a Valparaiso beach we should find that the temperature

of the sand at the surface (half-inch deep) was about 112° F., and at a

depth of four inches about 80°. This would be above the average for the

zone, which would be probably near the typical summer-temperature of an

English beach, namely, 102° at the surface and 77° four inches down.

This subject of beach temperature is discussed in Note 70.

Plants typical of the beaches of this zone, and evidently occurring over

the length of it, are Convolvulus soldanella, Nolana (paradoxa?);

Polygonum maritimum, Salsola Kali, and Selliera radicans. Nolana is a

Chilian and Peruvian genus. This beach plant, which is especially

abundant on the beaches near Coronel and at Bahia San Vincente, has the

creeping habit of its associate, the Convolvulus. However, it possesses

seeds, or rather seedvessels, of more limited buoyancy; and it is shown

in Note 71 that prolonged drying is needed for effective dispersal by

currents over great distances. This beach species of Nolana has narrowly

escaped being a widely-spread littoral plant; whereas it is now

restricted to the Chilian beach flora. Selliera radicans, a little

creeping Lobeliaceous plant, growing under the shade of tall clumps of

Juncus at the edge of the beach or in wet places where springs ooze out

in the sand, is a very interesting species that occurs also on the other

side of the Pacific in Australasia. Of the mode of dispersal of its

small seeds I know nothing, as the fruits were not ripe at the time of

my visit; but I would suggest that some resident botanist should

investigate this important point. I found it at Corral and at Coquimbo;

and Gay speaks of it as growing on wet coast places from Chiloe to

Coquimbo, a range of 12-1/2° of latitude.

It is probable that all the shore-plants of this zone extend south to

Chiloe in latitude 42° S.; and it is likely that some of them reach

towards the Straits of Magellan. I did not find any of them within the

Straits on the beaches in the vicinity of Punta Arenas, where, however,

I noticed the three plants recorded by Ball, namely, Armeria maritima,

var. andina; Senecio candidans, also found in the Falkland Islands; and

Plantago maritima; besides a Chenopodiaceous plant not in fruit. The

Plantago has no capacity for dispersal by currents, and probably none of

the other plants are thus dispersed. I formed the opinion when in the

Straits that the beach plants on the Pacific and Atlantic coasts of

Patagonia could have but little communication by the currents, and that

they are in this respect quite cut off from each other. A botanist who

investigates the strand-flora of Patagonia and Tierra del Fuego in

connection with the littoral plants of the opposite coasts ought, if he

has not already done so, to obtain some very interesting results from

the standpoint of plant-dispersal.

The northern limit of the plants of this zone near Coquimbo, in lat. 30°

S., is not determined by the change in climatic conditions that goes

normally with decrease in latitude, but by the vicinity of the great

deserts of Northern Chile, the aridity extending to the beaches.

Amongst the other plants occurring generally in the Convolvulus

soldanella zone of Southern Chile, species of Salicornia and Samolus are

to be observed in wet places. On the beaches near Valparaiso and in the

vicinity of Talcahuano there thrives a species of Franseria, a Composite

plant possessing prickly fruits well suited for conveyance in bird’s

plumage, but not adapted, as shown in Note 71, for dispersal by

currents. Mesembryanthemum is a typical beach-plant at Coquimbo, and an

intruder from the adjoining hill-slopes at Valparaiso. Raphanus,

seemingly R. maritimus, occurs in places, but apparently only as an

intruder from the cultivated districts behind the beaches. One or two

species of Euphorbia are not uncommon. A few small trees or bushes of

Acacia farnesiana grow typically on the beach at Coronel and in

neighbouring sandy tracts at Talcahuano, though the plant, as Gay

observes, has been introduced. Sophora tetraptera, found also in New

Zealand, and one of the most interesting plants of the Antarctic flora,

thrives as a small tree on the hill slopes overlooking the harbour of

Corral, becoming bushy where in places it intrudes on the beaches, and

fruiting there as freely as on the slopes above. It was by testing the

buoyancy of the seeds of this plant that I was led to the discovery of

its mode of dispersal by the currents (I am indebted to Mr. Holland for

the specific determination of the fruits sent by me to the Kew Museum).

Other shore-plants, of course, occur in this zone; but I have gone far

enough to illustrate the subject. Of the numerous occasional intruders

from the neighbouring inland districts, frequently Compositæ, I say

nothing. The results of my observations on the floating power of the

seeds and seed-vessels of some of the shore-plants of this zone are

given in Note 71.

Stranded seeds and fruits that belong to the proper beach-drift are not

easily found on the beaches of Southern Chile, as they are often buried

in rubbish. Those most characteristic are seeds of Convolvulus

soldanella and drupes of Nolana (paradoxa?), both typical beach-plants

of the zone. Portions of Salsola Kali bearing mature fruits, as

described in Note 17, are also frequent. Seeds of Sophora tetraptera

were found on the beach of Bahia San Vincente, whither they must have

been brought by the Humboldt Current from the south, as I did not

observe the tree in the vicinity. On this beach, as well as at

Valparaiso, the prickly fruits of Franseria were abundant in the drift,

doubtless derived from the plants growing on the same beaches. In

addition we get as frequent components of the beach-drift materials that

mark the white man’s presence over much of the globe. Corks are widely

distributed over the beaches of the world; but on no coast have I found

them more numerous than on the Valparaiso beaches. Here we find Medicago

fruits, the empty stones of the cherry, the plum, and the peach, empty

filberts and other materials, all of which I have gathered on the shores

of the Straits of Messina and on English beaches. Amongst this medley we

find also Casuarina cones and fruits of Eucalyptus. Then we find special

indications of the New World in the pea-nut (Arachis hypogæa) and in the

abundant seeds of a huge pumpkin (Cucurbita), which is a favourite food

with the Chilian indigenes. These seeds are cited as an example of

futile buoyancy in Chapter XIII.

THE PLANTLESS OR DESERT ZONE (NORTHERN CHILE).

This zone of the coast, which stretches north for some 700 miles from

Coquimbo to near Arica (30°-18°30ʹ S. lat.), corresponds to the great

desert region of North Chile. On the beaches of Antofagasta, Tocopilla,

and Iquique, which are situated in the midst of this zone, I found no

plants. This rainless sea border of barren mountains, presenting to the

eye of the traveller from the deck of a passing steamer nothing but rock

and sand, must be one of the most desolate coasts on our globe. It is

therefore not a matter for surprise that the beaches are of dry loose

sand in which the hand fails to find on scooping below the surface that

refreshing coolness which is the character of beaches in all latitudes

where the land is vegetated and a subsoil drainage seaward exists. Under

ordinary conditions the sensation of moisture in the sand a few inches

down is not produced by the mere proximity of the sea. On the

Antofagasta and Iquique beaches the temperature in the heat of the day

of the surface half inch ranged from 120° to 130° F., whilst four inches

down it was 95° to 100°, and no moisture was found by scooping five or

six inches down. On the Taltal beach, which lies towards the southern

end of the desert region, I noticed, besides a few plants of Suæda

fruticosa, two other species of the orders Santalaceæ and Nolanaceæ,

evidently intruders from the inland regions. Where the zone of extreme

aridity terminates at the north between Pisagua and Arica a few bushes

are to be seen on the hill-slopes behind the beaches.

Very little seed-drift came under my notice on the beaches of the desert

zone. Here and there I found a few Medicago pods and some seeds of the

large pumpkin above noticed, but that was all. This is due as a rule to

the seed-drift being masked by an enormous amount of rubbish, mostly

brought from the south by the Humboldt Current. My walk for five miles

along the beaches immediately north of Antofagasta gave me an experience

in the way of stranded drift such as I have never met with on the

beaches of any other region. All the dead bodies of the Chilian coast to

the southward seem to have been stranded in the bend of Moreno Bay, on

the shore of which Antofagasta lies; and the air was tainted with

decaying flesh, the past being mixed up with the present in a most

unrefreshing fashion. Besides carcases of sea-lions, six feet in length,

sharks, dog-fish, and fish of many sorts, some of them dried up, others

in a state of putrefaction, there were dead penguins, dead pelicans,

dead sea-birds of other kinds, the bodies of horses, cattle, dogs, &c.,

all preyed upon by the numerous vultures and skuas, and in some

localities by hungry-looking dogs of large size that took no notice of

me as they slunk along. The past was represented by great quantities of

bones that lay bleaching on the sand, with here and there a vertebra of

a whale, making in all quite a varied osteological collection. But this

was not all. Carcases of all sorts were drifting towards the beach. Here

a vulture, there a skua, there again a dog stood just beyond the

tide-wash looking keenly seaward; and by following the direction of

their gaze one could see that each had marked down a carcase slowly

drifting in. Now and then they would make a dash, scarcely waiting for

the new arrival to be washed up by the waves. But there was no

competition, since there was enough for all.

Under such conditions my investigation into the seed-drift was out of

the question; but I saw what would be considered by some as more

interesting, namely, the dead of many latitudes piled up on the beach by

the Humboldt Current.

THE SESUVIUM ZONE (THE PERUVIAN COAST).

This zone, which comprises the whole Peruvian sea-border from Arica in

18°30ʹ S. to the vicinity of Tumbez in about 3°30ʹ S., usually possesses

in its scanty littoral flora one or two species of Sesuvium, and in some

places Sesuvium alone occurs on the beach. The beaches here do not line

a region of almost complete aridity, as in the coast corresponding to

the great desert region of North Chile. Though here also scarcely any

rain falls, the sea-border receives the benefit of the “garuas” or

drizzling sea-fogs; whilst the region immediately behind the coast may

either be desert or semi-sterile during much of the year, or may be

scantily vegetated, or, as along the river-valleys, may display a

vegetation more fitting to the latitude. The general aspect, however, of

the coast of Peru is one of aridity; but there are probably few beaches

where a certain amount of subsoil drainage from the land sea-ward does

not exist. This is well exhibited at Ancon, north of Callao, where in

the most unlikely situations water is reached by digging wells; but in

spite of this the Sesuvium alone grows on the beach. The beaches

examined by me in the heat of the day in February, as at Mollendo and

Ancon, had much the same surface-temperature noticed in the preceding

month on the beaches of North Chile, namely, 120° to 130° F., and in one

place 135°; whilst at a depth of four inches the sand was rather cooler,

and instead of being between 95° and 100°, as on the Antofagasta and

Iquique beaches, it was here usually only about 90°. But it was only

occasionally that the sand felt at all moist at a depth of five or six

inches; and in this zone, therefore, only a few shore plants of a

peculiar type could be expected to find a station on the beaches,

excepting, of course, those localities where low marshy districts or

lagoons lie behind the beach.

The beach plants of the coast of Peru as observed by me though usually

scanty, presented two types according to the character of the district

bordering the beach. I make no mention here of those local plants, often

belonging to the Compositæ, that as at Callao and Arica descend the

valleys to the beaches, or to those numerous introduced plants that

accompany cultivation, such as we find at Arica. In those coast

localities, as at Arica, Callao, and Chancay, where salt-water pools or

brackish lagoons lie behind the beach, or where a stream or a river

empties into the sea, Sesuvium portulacastrum, Heliotropium

curassavicum, and a Salicornia are to be generally noticed, and, as at

Callao, Batis maritima may also abound. On the Chancay coast, about 30

miles north of Callao, there lies inside the shingle-beach a large

shallow lagoon of brackish water (spec. gr. 1·012) with extensive muddy

marginal flats, the temperature of the water at the edge being at

mid-day on Feb. 3rd, 90° F. In the water flourished Ruppia maritima,

which was also exposed in dead, dry, matted masses on the bordering

mud-flats. On these mud-flats grew Sesuvium portulacastrum, which near

the water’s edge was associated with a small species of Salicornia,

whilst further away from the water it was accompanied by Heliotropium

curassavicum.

But the most typical beach-flora of the Peruvian coast is such as we

find on the dry beaches skirting the base of sand-covered or barren

hill-slopes such as occur at Mollendo, Ancon, and Paita. As at Ancon,

sand-covered hills and plains may extend miles inland, displaying here

and there lines of shifting sand-mounds or “medanos.” On such beaches we

may often find only a solitary plant, a species of Sesuvium which seems

to differ only in its larger flowers, its much larger leaves (2 inches

long), and its stout stems, of the thickness of the little finger, from

the ordinary Sesuvium portulacastrum. This seems to be the only plant

that can make its home on such beaches. At Mollendo, where there are

signs of desiccated pools behind the beach which are occasionally filled

with sea-water, the vegetation was of an intermediate character and more

abundant; and here grew Sesuvium portulacastrum, a tall Salicornia, and

Suæda fruticosa; whilst the commonest plant was a prostrate Nolanaceous

species with a handsome purplish flower.

Excepting with the fruits of Batis maritima, and perhaps the buoyant

joints of Salicornia, scarcely any of the prevailing shore-plants of the

coast of Peru possess a capacity for dispersal by currents. In this zone

I rarely found any seed-drift on the beaches. Much rubbish, such as

roots of bamboos, however, may be brought down by the rivers; and where

the Humboldt Current strikes a bend in the coast we get a repetition, on

a smaller scale, of the scenes on the Antofagasta beaches. Ancon Bay,

for instance, receives much of the floating offal of the south.

THE MANGROVE ZONE (THE COASTS OF ECUADOR AND COLOMBIA)

We come now to the mangrove zone which comprises, with the remarkable

exception of a long stretch of arid sea-border to the north of the Gulf

of Guayaquil, the whole remaining western sea-border of South America,

namely, the Ecuadorian and Colombian coasts. My own acquaintance with

this region is limited to the estuary of the Guayas or the Guayaquil

River and to the southern shore of the Gulf of Guayaquil; but I am able

to avail myself of the researches of Baron von Eggers, which cover the

entire Ecuadorian coast; and with Ecuador, therefore, I will bring this

brief sketch of the littoral flora of one side of a large continent to a

conclusion.

The Ecuadorian coast, lying, as Baron von Eggers observes, between the

rainless and desert coasts of Peru and the “ewig grüne” coasts of

Colombia, may be regarded as a transition-area presenting very varied

and complicated conditions. With the cause of the remarkable contrasts

exhibited by the strand-flora, not only on the coast of Ecuador, but

along the whole west coast of South America through some forty-five

degrees of latitude from Patagonia to Colombia, I will presently deal.

Here it may be remarked in passing that the Humboldt Current has played

the determining part in producing the abnormal climatic conditions to

which these remarkable contrasts in the strand-flora of this coast of

the continent are mainly due.

The mangrove zone, marking a more or less abrupt transition from a

region of drought and semi-sterility to one of humidity and rank

tropical vegetation, begins about lat. 3° 30ʹ S., that is, in the

vicinity of Tumbez, or perhaps nearer the boundary-line between Ecuador

and Peru in lat. 3° 20ʹ (see Note 72). Occupying the southern shore of

the Gulf of Guayaquil it extends up the Guayas estuary to Guayaquil and

rather beyond. But when we follow the coast of Ecuador northward from

the island of Puna towards Santa Elena Point, we come upon one of the

most remarkable phenomena presented on the west coast of South America.

The dry region begins again and the mangroves disappear; and these

conditions continue through about 2-1/2 degrees of latitude until we

reach the equator, when the mangrove zone soon recommences, and, as I

infer, continues northward without a break to the coast of Central

America.

Dealing first with the mangrove districts of the south side of the Gulf

of Guayaquil and of the Guayas or Guayaquil estuary, we may observe that

probably in few localities of the globe have the forces of nature worked

more in unison to produce the conditions favouring the growth of the

mangrove. The reason why this particular locality has been thus favoured

will be discussed later on in this chapter. I may here observe that

Baron von Eggers was so struck with the exceptional features of the

mangrove-growth in this region that he was inclined to look for the

American centre of the genus Rhizophora, the prevailing mangrove, in the

estuary of the Guayas River.

I will not enter into a detailed description of the mangrove-formation

of this coast, which has indeed been given by the German botanist; but I

will merely refer to the leading features such as they presented

themselves to me. In the first place, reference will be made to the

sea-border of the province of Eloro, where I spent nine or ten days,

making Puerto Bolivar, the port of Machala, my headquarters—a locality

about thirty miles east of Tumbez. Except in the Guayas estuary I have

never seen such a magnificent growth of mangrove.

By following the line of light railway that runs about six kilometres

inland from Puerto Bolivar to Machala, the capital of the province, we

obtain a good section of the mangrove-belt, which may be thus described.

The mangrove-swamp proper extends about three kilometres inland. Whilst

the small variety of Rhizophora mangle (mangle chico) immediately fronts

the sea, Laguncularia grows on the islets close to the seaward margin of

the swamp. When we enter one of the numerous broad creeks that intersect

the border of the mangrove-belt we soon find ourselves in the true

mangrove forest, where prevail tall trees of Rhizophora mangle (mangle

grande) that rise to a height of 70 or 80 feet or more. Gloomy as the

depths of the swamp are, they acquire quite a funereal aspect, the

branches of the trees being draped with pendent Tillandsias. These long,

hair-like, tangled growths hang vertically from the branches of the

trees and may be 20 or 30 feet in length. In the rear of the zone of

tall mangroves we come upon a more open district of the swamp. The

forest proper gives place to a tract occupied by small trees of

Rhizophora, Laguncularia, and Avicennia, with here and there whole acres

occupied only by the shrubby Salicornia peruviana which attains the

height of a man.

[_To face page 484._

[Illustration:

Emery Walker sc.

Rough Plan of the Gulf of Guayaquil.

]

(The main stream of the Humboldt current, as indicated by the arrows,

turns off to the north-west at Cape Blanco; whilst a small branch

crosses the mouth of the Gulf of Guayaquil and flows along the Ecuador

coast north of Santa Elena Point.)

Here terminates the mangrove-swamp proper, and about three kilometres

from the sea it passes gradually into a region of extensive bare

mud-flats which are penetrated by salt-water creeks, two or three yards

across and a foot or two in depth, that are bordered by low and shrubby

Avicennias, the Salicornia bushes above noted, and dwarfed trees of

Rhizophora mangle only four or five feet high. These flats, which are

evidently only overflowed by the sea at the higher spring tides, were at

the time of my visits much sun-cracked and in some parts incrusted with

salt; but the mud was rather soft, and in places Sesuvium portulacastrum

and Batis maritima flourished in quantity on it. These mud-flats, about

two kilometres across, pass by degrees into the low-lying level district

known as the Machala plains, on which the capital of the province is

built. Here the soil is dryish, and, notwithstanding that it displays on

its surface when exposed to the sun a white saline efflorescence, a dry

jungle type of vegetation of the xerophilous character here thrives. I

noticed casually the Algaroba (Prosopis), a yellow-flowered Cordia,

cacti of the Opuntia and Cereus kinds, besides several small trees and

shrubs often thorny.

These Machala plains, on account of the fine saline incrustation above

mentioned, are of much interest, since at a distance of six kilometres

from the coast they thus display on their surface the effect of

sea-water infiltration, their level above the sea being only a few feet.

We have seen the three stages of this infiltration landward of

sea-water: first, the mangrove-swamps daily overflowed by the tide;

second, the mud-flats behind them which are only overflowed by the

fortnightly spring-tides; third, the vegetated plains behind all, which

are sufficiently raised to be above the reach of the tides, but which

are nevertheless soaked with sea-water that displays its presence in the

salt left by evaporation on the surface of the soil.

But another interesting point is here raised. At the back of the

mangrove-belt, in most parts of the world, we usually find a

particularly rank and luxuriant vegetation where the Scitamineæ often

take a leading part; whereas on the sea-border of this part of Ecuador

the mangrove-swamps pass gradually into arid saliniferous plains. With

this singular fact is to be associated the circumstance that we see here

in operation, some four or five miles from the coast, a process by which

great quantities of sea-salts are accumulating below the surface. This

may possibly be concerned with the origin of the great saline deposits

of Northern Chile. However this may be, there is some reason for

believing—and I understand that this is the opinion of Dr. Wolff, the

historio-geographer of Ecuador—that in the course of ages the tendency

will be towards an extension of the dry, sterile regions of Northern

Peru into Ecuador. This subject is referred to again in a later page of

this chapter.

Whilst in this neighbourhood I made the ascent for some fifteen miles of

the Santa Rosa River, which opens into the sea near Puerto Bolivar. It

is a tidal estuary that has no proportion in size to the small river

that enters it. In its lower third we passed at first between long

mangrove-islands formed almost entirely, as viewed from the boat, of the

tall Rhizophora trees draped with Tillandsias, and presenting really a

magnificent spectacle. In the middle third we were penetrating into the

rear of the mangrove-belt. The giant swamp-fern (Chrysodium aureum)

abounded, and here and there we passed by a patch entirely held by the

large shrubs of Salicornia peruviana. The tall Rhizophora trees were

replaced by the short variety, the “mangle chico,” which ceased

altogether about ten miles from the mouth of the estuary, but probably

only about five miles from the nearest part of the coast. The water at

the place where the Rhizophora trees ceased was evidently quite fresh

during nine out of the twelve hours, being only salt in the latter part

of the rising tide. Above the mangroves, in the upper third of the

ascent, Hibiscus tiliaceus, with Chrysodium aureum, flourished on the

banks. The shallows at the margins were occupied by a considerable

variety of semi-aquatic and other plants, such as Pontederia (two

species); one of the Alismaceæ, with the flower and fruit of Sagittaria

and the leaves of Alisma; Typha, Polygonum, and an Amaryllid like

Crinum. Plants of Pistia and Pontederia floated in the stream.

I have said enough to give a general idea of the composition of the

mangrove-belt of the Ecuador littoral, and will refer but briefly to the

mangroves and other river-side plants in the neighbourhood of the city

of Guayaquil, some forty miles up the Guayas estuary. As I have remarked

in Note 38, the water of the river off the city is usually quite fresh

except at high water; but the sea has much freer access to the channels

at the back of Guayaquil, where at high water the density was 1·014. In

these channels are displayed the typical mangrove formation, trees of

Rhizophora mangle bordering the water, whilst behind they are mingled

with Avicennia tomentosa and Laguncularia. On the banks of the main

river, where they are overflowed at high water, Anona paludosa was the

most frequent tree, being associated with the Rhizophora, Hibiscus

tiliaceus, and other trees. Above the city, Polygonum glabrum was

growing in dense masses at the river’s edge, whilst Pontederia and

Pistia flourished on the low muddy banks and floated in quantities in

the river.

Before quitting the subject of the mangrove-formation of Ecuador, I will

refer shortly to the two varieties of Rhizophora mangle that here occur.

Baron von Eggers received the impression that the common type of this

species, a low tree bordering the coast, did not exist in Ecuador, such

a type as he says is characteristic of the West Indies and of Central

America, and, I may add, also of Fiji. The species he regards as

acquiring a new facies in Ecuador, where it exists as tall forest-trees,

branchless for half their height, and exhibiting other divergent

characters. However, I found that the common type of the species occurs

normally on the coast in the vicinity of Puerto Bolivar, thirty miles

east of Tumbez, a district above described.

There are two distinct forms of Rhizophora mangle exhibited in the

mangrove-belt of the coasts around Puerto Bolivar. One of them, which

the indigenes name “mangle chico,” is a small tree, 10 to 15 feet high,

with useless timber, that immediately borders the sea, and, in fact,

largely forms the margin of the swamp, not only on its seaward side, but

also on the land side, where it passes into drier ground. The other, the

“mangle grande,” a tall tree reaching to 60 or 80 and sometimes perhaps

to 100 feet in height, composes the interior, and indeed the bulk, of

the mangrove-belt, and possesses a hard and durable timber much employed

in the district.

Distinct as these two types are, it is not difficult to find

intermediate forms, and, in truth, in some localities they prevail. But

the interesting point is that this peculiar Ecuadorian type of the

species, a type that attracted the attention of the eminent German

botanist, comes near the “Selala,” the mysterious seedless Rhizophora of

the Fijian swamps—a subject fully discussed in Chapter XXX., where I

have compared the Fijian and Ecuadorian Rhizophoras. Both the “Selala”

of Fiji and the “mangle grande” of Ecuador are intermediate between the

American Rhizophora mangle and the Asiatic R. mucronata, resembling the

last in their inflorescence, but in other points approaching the

American species. The “Selala,” however, comes nearer to the Asiatic

tree, whilst the “mangle grande” comes nearer to the American tree.

Unlike the Fijian tree, that of Ecuador is not sterile, but matures its

fruit; and it displays no evidence of the vegetative reproduction so

characteristic of the “Selala.”

Sandy beaches are not common on the mangrove-fronted shores of the south

side of the Gulf of Guayaquil. However, on the seaward side of the long

low mangrove island of Jambeli, on which the lighthouse is placed off

Puerto Bolivar, there is a long stretch of beach of whitish, mainly

non-calcareous, sand. The Coco palms behind the beach give the coast

quite the aspect of a Pacific island strand. Ipomœa pes capræ flourishes

on the sand nearest to the sea; and immediately behind, the beach is

more or less occupied by a Cyperus 2 to 3 feet high, and by Canavalia

obtusifolia. Further back grows a small Acacia tree, and behind it the

yellow-flowered Cordia tree of the district; and in the rear of all lie

extensive mud-flats, partly occupied by stunted bushes of Avicennia

tomentosa and by Sesuvium portulacastrum, which in their turn pass into

the mangrove-swamps.

On account of the enormous amount of drift of all descriptions that is

carried to the sea by the Guayas or Guayaquil River, floating vegetable

materials are abundant in the Gulf of Guayaquil, and are thrown up in

quantity on the coasts of Ecuador. One of the most interesting

spectacles at Guayaquil is presented by the floating river-drift. Huge

tree-trunks and floating islets, the last-named ranging from 3 or 4 to

30 or 40 feet or more across, were, at the time of my visit in February,

being carried to and fro unceasingly in front of the city by the tide,

gradually making their way down the river, and ultimately reaching the

open waters of the gulf. Floating plants of Pistia were in abundance;

and their fate when they reached the sea must have been tragical. The

islets were exceedingly interesting; they were evidently formed of

materials lifted up bodily from the shallows at the margin of the river,

and then carried off in the stream. They were mainly composed of two

species of Pontederia and of Polygonum glabrum in the position of

growth; the first often in flower. Pistia and a variety of smaller

plants nestled among them, such as Salvinia, portions of Azolla, Lemna,

&c.; and in one islet I noticed, oddly enough, the growing rhizome of a

sensitive plant (Mimosa pudica). A great quantity of floating seeds

collect amongst the roots and stems of the plants composing the islets,

and here I obtained much of the smaller seed-drift.

Most frequent in the floating drift of the river at Guayaquil were the

seeds of Anona paludosa, often in a germinating condition. The seeds are

liberated by the decay of the floating fruit, which was also common in

the drift. Amongst the larger materials were the seeds of Entada

scandens and of Mucuna; the empty seeds of the vegetable-ivory palm

(Phytelephas macrocarpa), the sound seed possessing no floating power;

the “stones” of Spondias lutea, L., as identified by Mr. Holland, of the

Kew Museum; the empty small nuts of several palms, including,

apparently, Oreodoxa, &c. Amongst miscellaneous materials were small

gourds, which are referred to in Note 47, and an occasional empty cacao

fruit. Smaller seeds were also abundant, and included those of Hibiscus

tiliaceus, Erythrina, Vigna, Ipomœa, and others. Carried into the river

from the neighbouring mangrove-creeks, where they abound, there were

floating seedlings of Rhizophora and Avicennia, fruits of Laguncularia

often germinating, and the seeded joints of Salicornia peruviana.

There was of course, in addition, much that was strange in the floating

drift of the Guayas River, which received its contributions not only

from the river-side vegetation and the neighbouring mangrove-swamps, but

also from the interior mountain ranges culminating in Chimborazo, the

slopes of which are drained by its tributaries. I had several

opportunities of meeting the drift of the Guayas River in the open

waters of the Gulf of Guayaquil. Much of it is carried along the south

side of the gulf; and I picked up at sea, ten to twenty miles from the

mouth of the estuary, many of the things above enumerated, such as

Erythrina and Mucuna seeds, seeds of Hibiscus tiliaceus, the empty

vegetable-ivory seeds, the seedlings of Rhizophora and Avicennia, and

the germinating fruits of Laguncularia and Salicornia peruviana. Much of

these materials mingled with local drift is stranded on the long beach

of Jambeli Island, thirty miles from the mouth of the estuary. Here,

besides the seeds of Canavalia obtusifolia and Ipomœa pes capræ derived

from the locality, I found the seedlings of Rhizophora and Avicennia,

and the fruits of Laguncularia and Salicornia peruviana, that might have

been in part derived from the adjacent swamps, as well as much of the

drift of the Guayas River, such as the seeds of Anona paludosa, Entada

scandens, Erythrina, and Mucuna, the small gourds, the same small

palm-nuts, the empty seeds of Phytelephas, the “stones” of Spondias

lutea, and much other material previously familiar to me, but nowhere a

sign of the floating Pistias and of the flowering Pontederia islets of

that estuary.

_The Stretch of Dry Coast from the Vicinity of Puna Island to the

Equator._— This remarkable piece of sea-border, covering nearly three

degrees of latitude, and in its aridity and general character recalling

the sterile sea-coast of Peru, is placed between the humid

mangrove-fronted coast of the Guayas estuary and the similarly humid and

mangrove-fronted coasts of Northern Ecuador and Colombia. The mangrove

seems to be almost absent from this stretch of dry coast. Mr. F. P.

Walker, of the Santa Elena Cable Station, tells me that some time ago a

little mangrove-growth existed near the Point, but that it has

disappeared; and Baron von Eggers implies the absence of mangroves from

the whole coast. The first-named speaks of the dry character of the

coast district from Santa Elena Point to within half a degree of the

equator; and the last-named, in his description of the coast, mentions

cacti and thorny plants as typical of the vegetation. Since this region

represents a typical locality where the direct influence of the Humboldt

current on the climate of almost the whole west coast of South America

can be put to the proof, I will refer to its peculiar climatic

conditions below in my discussion of the general question, and will here

content myself with saying that on this dry portion of the coast of

Ecuador we have reproduced, but in a less pronounced degree, the

climatic conditions of the coast of Peru.

_The Humboldt or Peruvian Current and the Climate of the West Coast of

South America._—The question we will now briefly consider is one that is

concerned with the determining causes of the singular distribution of

coast-plants on the west coast of South America. The reader will have

already seen that the matter is an affair of climate; but it is an

affair of climate in which (although it affects forty or more degrees of

latitude), latitude, in a general sense, scarcely counts. All the

naturalists, from Humboldt onward, who have sojourned in this region of

the globe have displayed a deep interest in this subject; and I suppose

there can be no region of the globe where there are so many climatic

anomalies as interesting to the meteorologist. Here, for instance, might

be obtained materials for solving the irritating mystery of a London

fog; and if the suggestion of Baron von Eggers, before alluded to, is

carried out, and a station is established by the Meteorological

Societies of Europe and America at some suitable locality like Santa

Elena on the coast of Ecuador, we might obtain, among other results,

another line of investigating the causes of the fogs of our metropolis,

a subject about which Captain Carpenter has recently made an important

preliminary inquiry.

I will assume that my readers are already acquainted with the nature of

the problem to be discussed relating to the climate of the west coast of

South America, and that they are familiar with the view generally held

that the aridity of this extensive coast region, stretching from the

thirtieth parallel of south latitude to the equator, arises from the

loss by the trade-winds of all their moisture in the interior of the

continent before reaching the western countries of Chile and Peru. Mr.

Ball, in his book on South America, opposed this view, though from

reasons only partially valid, since he instanced the Ecuador coast as

being, contrary to the theory, a wet coast, whereas we know that a large

stretch of it is arid and not unlike Peru. The parting of the ways in

this discussion lies in the answer to the query, Why should the

south-east trade carry so much moisture to the east side of South

America, whilst the south-west winds, that are equally prevalent on the

west coast of the continent, are drying winds which convert the

sea-border into a desert, as in Northern Chile, or into a region of

semi-sterility, as in the instance of Peru? Other things being equal, we

should expect both sea-borders of the continent in these latitudes to be

well watered. In the answer to the question why the south-east trade

should be a wet wind and the south-west wind a dry one lies a fatal

objection to the prevailing view.

When Professor Davis, in his article on North America in the

_Encyclopædia Britannica_ (vol. 25), observes in connection with the

arid coast regions on the west side of the continent that the southerly

flow of the winds along the Pacific coast gives them a drying quality,

thus causing the extension to the coast in South California and in North

Mexico of the arid regions of the interior, he seems to imply that these

winds acquire their drying capacity in flowing from cooler to warmer

latitudes. On this view all trade-winds should be drying winds, whereas

the reverse would appear to be the case.

There is some condition, present on one coast of the South American

continent and absent on the other, which determines why a southerly

wind, blowing landward, is in the one case moist and in the other dry.

According to my own view the winds of the arid coast regions of western

North America cross the cool waters of the Californian current, and thus

acquire their drying quality on striking a sea-border more highly heated

than the winds themselves. On the tropical west coast of South America

the winds also become drying winds by passing over the cold waters of

the Peruvian or Humboldt current, where mists are in consequence of

frequent occurrence; and on striking the more highly heated land-surface

at the sea-border the moving air does not part with any more moisture

until an altitude of some thousands of feet above the sea is reached,

when the cloud-belt forms. On the mountains bordering the coast of the

Antofagasta province, in January, the clouds gathered at an elevation of

4,000 to 5,000 feet. Perhaps the best way to contrast the east and west

coasts of tropical South America in this respect would be to say that

whilst the wind blows landward in both regions, the land is the

condenser on the east side, and the sea, owing to the interposition of

the cold Humboldt current, is the condenser on the west side.

During a fortnight spent in February at Ancon, about twenty miles north

of Callao, I noticed that with the prevailing cool south-westerly wind

the coast was clear, but it was misty at sea. On the few days when there

were warm westerly and north-westerly breezes, the weather was thick at

sea; and if this condition was pronounced, the whole coast was enveloped

in mist; but more usually the coast-line was fairly clear except at the

promontories, along the sides of which clouds blown in from the sea

rolled in lines inland, not generally attaining an elevation over 300 or

400 feet, but sometimes reaching 900 or 1,000 feet, and gradually

disappearing a mile or two inside the coast-line. These sea-born clouds

thus vanished as they traversed the more highly heated land-surface; and

the air-current continuing its inland course mounted the slopes of the

adjacent mountain ranges of the Andes, some three or four miles from the

coast, until at an altitude of some 5,000 or 6,000 feet condensation

again occurred and the cloud-belt was formed at those cooler levels.

From the summit of a range rising to a height of about 2,500 feet to the

north-west of Lima I had presented to me a splendid spectacle, on

February 12th, in the formation of the coast-belt of clouds. The

forenoon was clear, but about 2 p.m. the sea-born clouds began to roll

inland, concealing the lower two-thirds of the island of San Lorenzo,

which has an elevation of almost 1,400 feet, and completely covering up

Callao and the low country bordering the sea, but extending only a mile

or two from the coast-line. The dense cloud that covered Callao

appeared, as I looked down upon it from my mountain-peak, like a billowy

field of snow sparkling in the sun, with the summit of San Lorenzo

standing out like some bare alpine summit from amidst the snows. Yet

beneath that dazzling covering Callao lay all in gloom; whilst only six

miles up the broad valley of the Rimac the city of Lima stood in a blaze

of sunlight, its domes and towers reflecting back the light as I looked

at the strange contrast it presented with the buried city of the coast.

The mystery of a London fog seemed to lie unfolded at my feet, ready for

the man who can read the signs aright.

That the mere presence of a cold current on a coast with the winds

blowing off the land (as in the case of the Labrador current, which

extends down the Atlantic coast of North America to Cape Hatteras and

beyond) produces no sterilising effect on the vegetation of the

sea-border of a continent is well brought out in the beautifully

executed maps in Prof. Russell’s recent work on North America. The

essential condition for producing sterility on the sea-border of a

continent is not only that the waters of a cold current should wash its

coasts, but that the regular winds should blow landward across its cool

surface. These are what we find on the west coast of South America.

Not with the hope of adding anything new to our knowledge of the

climatology of this region, but with the purpose of becoming personally

acquainted with the problem involved, I paid considerable attention to

this subject during the three months passed on the west coast of South

America between Port Valdivia and Guayaquil. It was not until I had

dropped my thermometer into the cool water of the Humboldt current and

had watched the formation of the fogs on the sterile coast of Peru that

the real nature of the problem presented itself. From the pages of a

work like Tschudi’s _Travels in Peru_ one acquires an excellent idea of

the extraordinary climatic conditions of this region, and the same may

be said of the narratives of Darwin and other travellers; but it is

necessary to be brought into personal contact with these conditions

before one can appreciate their significance.

As is well known, says Baron von Eggers, the Humboldt current explains

the anomalous climate of the coast of Peru, and one may add of North

Chile and Ecuador. The current, which represents the extension

northwards of the west wind-drift of the Roaring Forties (see Dickson in

_Encycl. Brit._, xxxi. 404; and Admiralty Current Charts of the

Pacific), begins on the coast between the 33rd and 40th parallels of

south latitude, according to the season. North of Valdivia, as we

approach Valparaiso, in lat. 33°S., the effect of its presence is at

once seen in the increasing dryness of the climate and in the alteration

in the character of the vegetation. It has, however, been shown that the

current needs the co-operation of the prevailing southerly and westerly

winds as they blow landward over its cool waters. On the coast of Peru

these moist winds often generate fog and mist as they cross the current.

They reach the coast as drying winds, having a temperature much cooler

than the lower coast regions; and the air-currents do not precipitate

any moisture on the land until an elevation of 4,000 to 6,000 feet is

attained where the cloud-belt is formed.

In order to establish this theory it is, however, necessary to show that

when the Humboldt current leaves the coast normal conditions of humidity

occur, to which the vegetation responds, and that when the current

strikes the coast again the conditions of aridity reappear. In its

course northward the current divides off Cape Blanco, the principal mass

of its waters making towards the Galapagos Group, whilst the remainder,

after crossing the Gulf of Guayaquil, flow along the coast of Ecuador

between Santa Elena and the equator. Now, it is along this stretch of

the Ecuador coast that the conditions of aridity reappear and that the

climate of the Peruvian sea-border is in a modified form reproduced. In

the interior of the Gulf of Guayaquil, on the other hand, where the

sea-border is no longer subjected to the influence of the cold waters of

the Humboldt current, the genius of the tropics, repressed through so

many degrees of latitude, bursts its bonds, and presents us with a

spectacle of littoral vegetation that, so far as mangrove-growth is

concerned, is probably unrivalled on our globe.

This contrast is well shown in the mean annual temperatures on the

opposite sides of the Gulf of Guayaquil. Baron von Eggers, quoting Dr.

Wolff, states that whilst the mean for the year at Puna is about 75° F.,

and at Santa Elena about 73°, on the south side of the gulf at Balao it

is several degrees warmer and is evidently not under 80°. The mean

temperature for the second week of March during my sojourn at Puerto

Bolivar, which is near the beginning of the mangrove region on the south

side of the gulf, was 79°, the mean daily range being 74° to 83·5°. This

stretch of dry coast reaching north from Puna to the equator is

evidently regarded by Baron von Eggers and others who have studied the

climatology of Ecuador as the critical area required to confirm the

theory connecting the aridity of the west coast of South America with

the Humboldt current. Here the sea for the greater part of the year has

a temperature (according to the British Admiralty chart of

surface-temperatures) of 70° to 75°; the mean temperature of the air is

73° to 75°; the rainy season, instead of covering a period of six months

and over, as in the humid regions north and south of this coast, has a

duration of only two or three months; the prevailing wind is south-west;

whilst the direct influence of the cool waters of the current is shown

in the general cloudiness that prevails during the last half of the year

and in the drizzling mists that are frequent from June to October.

Reference has already been made to the manner in which the vegetation on

this dry coast of Ecuador responds to the arid conditions, as, for

instance, in the absence of mangroves and in the prevailing character of

the plants of the sea-border, cacti, thorny plants, and such like. For

my information on this exceedingly interesting tract of coast, which is

the test-ground of the Humboldt current theory, I am indebted to the

papers of Baron von Eggers (see end of this volume) and to Mr. F. P.

Walker, of the Central and South American Telegraph Company’s Station at

Santa Elena, who very kindly communicated with me by letter. Some

additional remarks are given in Note 73, and my own observations on the

temperature of the Humboldt current from Antofagasta northward are

summarised in Note 74.

Before quitting the Ecuador coast a word may be said relating to the

prediction of Villavicencio that the climate of this sea-border will

assimilate itself to that of the rainless coasts of Peru. This is, I

believe, also the opinion expressed by Dr. Wolff in his _Geografia y

Geologia del Ecuador_ (Leipzig, 1892); and it is referred to by Mr.

Webster in his article on Ecuador in the seventh volume of the

_Encyclopædia Britannica_. There is a prevailing impression amongst the

more observing residents that I met in the Ecuadorian province of Eloro,

on the Peruvian border, that the country is drying up. A few pages back

I have described how in the Machala district of this province the

mangrove-belt passes landward into an arid region suggestive of the

sea-border of Peru. This transition is startling to one who expects to

find behind the mangrove-belt, as he would find in most parts of the

world, a humid region where Nature revels in the rank luxuriance of

plant-growth. This is, however, not always the case, since on the lee or

dry sides of the large islands of Fiji the mangrove-belt is backed by

extensive arid plains, for an explanation of which, as I have shown in

Note 22, we have to appeal rather to the hygrometer than to the

rain-gauge. This is true also of Ecuador; but whilst the reason is

intelligible enough in Fiji, it only carries us a step farther back in

the case of the Machala plains in Ecuador. These plains are continuous

with similar districts across the Peruvian border where they reach the

coast; and if the reader will refer again to my description of the

section of the mangrove-belt and the plains in its rear from Puerto

Bolivar to Machala, he will incline to the view that the desiccation of

the sea-border of Ecuador is now in progress.

Evidence of a more direct nature could doubtless be supplied by those

who have long resided on the coast of Ecuador, and in illustration I

will give an extract from one of Mr. Walker’s letters dated May, 1904,

from Santa Elena.—“The rainfall here might for the last ten years be put

down at two showers per year. It is said that the last good rainy season

was in 1891. The inhabitants say that formerly it always rained enough

to make the grass grow every year, but during the eleven years I have

been here there appears to be a marked falling off of the rainfall.”

It has been only possible to touch the fringe of this interesting

question here; but from the standpoint of the study of the littoral

flora of the west coast of South America it is of some importance.

Immediately behind the epoch of the present marine molluscan fauna of

this coast there lies an age when, as we learn from Philippi, the shells

of Chile were more akin to those of the Atlantic and Mediterranean

faunas than to those now found on the Chilian coasts. The transition is

a sudden one; and amongst other explanations of this strange

transformation Suess suggests the sealing up of a communication through

the Panama isthmus by volcanic eruptions and the appearance of the

Humboldt current (_Das Antlitz der Erde_, French edit. by Margerie, ii.

825). May it not be, my readers may ask, that the west coast of South

America is still in the age of progressive sterility; and that before

this age began Peru possessed a normal tropical strand-flora? It has

been remarked in Chapter VIII. that the same species of mangroves occur

on both the Atlantic and Pacific coasts of America, and that at all

events their present distribution belongs to an age when the Gulf of

Mexico was in communication with the Pacific Ocean. May we not, again,

suppose that in that age the mangroves extended far south on the coast

of Peru, just as they do now on the coast of Brazil?

Coral reefs are stated not to exist in tropical latitudes on the west

coast of South America in our own day; but we might almost expect that

at the close of the Tertiary period, and perhaps before the appearance

of the Humboldt current, they existed with the mangroves on the coast of

Peru. As bearing on the subject of a change of climate on that coast in

times geologically not remote, I may allude to the circumstance, which

is discussed more in detail in Note 75, that I found, sometimes in fair

quantity, blocks of massive coral, long since dead, much pierced by

boring shells, and in places undergoing a chemical change, at Arica

(lat. 18° 25ʹ S.), at Callao (12° 3ʹ S.), and at Ancon (11° 45ʹ S.) on

the coast of Peru.

These masses, which varied from a few inches to two or three feet in

size, gave me the impression of having been torn off the bottom, in some

cases in recent times, in others perhaps centuries ago, by the huge

sea-waves that from time to time overwhelm this coast. At Ancon, where

they were sufficiently abundant to be used for bordering the flower beds

in the hotel garden, they were most numerous in the vicinity of a rocky

spur of andesite that protruded from the beach between the tide levels

and was more or less covered at high water. A few paces inland from the

beach some of these coral masses, evidently stranded long ago, were

undergoing that queer process of disintegration which everything

calcareous seems to undergo on the beaches and plains of this almost

rainless coast. Like the bones of the Incas lying bleaching on the

neighbouring plains, like the sea-shells and bones of bird and beast

cast up long ago on the beach, they were falling to powder where they

lay, and the coral fragment lay often in the midst of its own _débris_.

The blocks on the beach proper were for the most part still hard and

compact, and the same may be said of those observed on the beaches of

Callao and Arica.

The corals were quite different from those with which I was familiar in

the reefs of the Pacific islands, and, bearing in mind the known

distribution of coral reefs, I was a little dubious about them.

Accordingly I sent some specimens to the British Museum, and Mr. Jeffrey

Bell has kindly informed me that they seem to be decayed and much

injured perforated examples of Porites. When powdered they effervesce in

an acid, but the bulk of the material remains undissolved.

No more eloquent testimony could be afforded of the rainless climate

than these corals crumbling on the Ancon plains when washed a few paces

inland from the beach. They could be noticed in all stages of

disintegration from the block surrounded by a little line of

disintegrated material, representing the initial products of its own

decay, to the crumbling mass, almost friable in the fingers, that was

lying in the midst of its own dust and loose polyp-tubes, and finally to

the little mound of _débris_ that alone remained. Mr. Darwin, in his

_Journal of Researches_ (chap. xvi.), refers to a similar process of

decay in the elevated shell-beds of San Lorenzo, off the coast of

Callao. On the higher terraces a layer of saline powder, consisting of

sulphates and muriates of lime and soda but with very little carbonate

of lime, was the sole indication of the shell-beds. Dry climatic

conditions at the sea-border evidently favour, as he observes, the early

decay of exposed calcareous remains.

_The Shore-plants and Stranded Seed-drift of the Panama Isthmus._

I spent two days at Panama and two days at Colon in examining the

neighbouring beaches and estuaries of the Pacific and Atlantic coasts of

the isthmus. On the Panama side the mangrove-belt was formed on the

seaward border of “mangle chico” (the small prevailing type of

Rhizophora mangle), Laguncularia, and Avicennia; whilst behind it passed

into extensive swampy tracts occupied by the Swamp Fern (Chrysodium

aureum), Hibiscus tiliaceus, and other plants. On the Colon or Atlantic

side the mangrove-belt had precisely the same composition and presented

the same species, Rhizophora and Avicennia usually forming the outposts

on the reef-flat, whilst Laguncularia was abundant in the rear. In the

estuary of the Rio Chagres, Rhizophora and Laguncularia were abundant

near the mouth, and Chrysodium aureum and Hibiscus tiliaceus by the

waterside higher up. Dr. Seemann, in his volume on the botany of the

voyage of H.M.S. _Herald_, observes that the species of Laguncularia

common on both the Atlantic and Pacific coasts of the Panama isthmus is

L. racemosa. This species differs in the form of its fruit from the

Ecuador tree. Laguncularia racemosa, Rhizophora mangle, and I may add

Anona paludosa and Conocarpus erecta, are all plants of the

mangrove-formation that occur not only on the Pacific and Atlantic

coasts of America but also on the west coast of Africa. It is likely, I

may add, that the “mangle grande,” the Ecuadorian type of Rhizophora

mangle, exists in the Panama isthmus, since in the higher part of the

estuary of the Chagres I found trees approaching it in characters.

Amongst the plants growing on the Panama beaches I noticed Canavalia

obtusifolia, Hibiscus tiliaceus, and Ipomœa pes capræ, all of which

occur also on the Atlantic side of the isthmus. The Manchineel

(Hippomane mancinella), found also on the Atlantic side of the

continent, grows on the Panama beaches. Its fruits, which look like

crab-apples, lose their outer fleshy covering when drying on the sand.

Not being familiar with this poisonous tree, I allowed some of the milky

sap of the fruits to touch the skin, and suffered great pain for five or

six hours. The fruit possesses an inner coat of air-bearing cork-like

tissue; and the stone, if I may so term it, thus acquires great floating

power. I kept some afloat in sea-water for five weeks, and no doubt they

will float for months.

The seed-drift to be observed stranded on the beaches and floating in

the estuaries on both sides of the isthmus is, generally speaking, the

same—a circumstance of great importance in plant-distribution, since we

can here see rivers bringing down the same seeds from the same “divide”

to the shores of the Pacific and Atlantic oceans. In the case of a plant

like Entada scandens, which grows in the interior, this is a matter of

much interest, as it thus possesses here a centre of dispersal from

which its seeds can be carried by the currents eastward to the West

African coast and westward across the Pacific to Malaya and (given time)

around the shores of the Indian Ocean to the East African coast. In

describing the possible routes of dispersion from this centre I have

described the distribution of the species.

I am indebted to Mr. Holland, of the Kew Museum, for the identification

of some of the drift-seeds and fruits collected by me on the isthmus,

those identified by him being followed by the letter H. On the beaches

and floating in the estuaries on both sides of the isthmus I found

Rhizophora seedlings; seeds of Entada scandens and Mucuna urens

(medic.), H.; seedvessels of Spondias lutea (Linn.), H.; Prioria

copaifera (Griseb.), H., with decayed seed; and the empty nuts, 1-1/2 to

2 inches in size, of more than one species of Astrocaryum, H. Although

in the case of the two last-named genera the seedvessels were useless

for dispersal, being evidently brought down from the interior by the

rivers, they serve to illustrate the important principle that the rivers

bring down the same seed-drift on both the Atlantic and Pacific coasts

of Central America. Mr. Hemsley includes amongst the seed-drift stranded

on the coast of Jamaica the seedvessels of Spondias (probably S. lutea)

and of Astrocaryum (_Bot. Chall. Exped._, iv. 299, 304).

Those of Spondias lutea were found by me floating in the Guayaquil River

and stranded on the beaches of Ecuador and of the Pacific and Atlantic

coasts of the Panama isthmus. This is the Hog-plum, which in tropical

America and the West Indies is both wild and cultivated. Its buoyant

“stone” has a covering of cork-like air-bearing tissue. This is a

remarkable case of non-adaptation in the matter of buoyancy. The

seedvessels cut across contained sound seeds; and they are provided with

the essential qualities of “long floaters.”

_Summary._

(1) The strand-district of the west coast of South America is divided

into four zones:—

(_a_) The Convolvulus soldanella zone of Southern Chile.

(_b_) The Desert or Plantless zone of Northern Chile.

(_c_) The Sesuvium zone of Peru.

(_d_) The Mangrove zone of Ecuador and Colombia.

(2) The mangroves do not extend south of Ecuador or, more strictly,

south of Tumbez (3° 30ʹ S.).

(3) The absence of mangroves on the tropical coasts of Chile and Peru is

attributed to the Humboldt current, which has so influenced the climate

that it has converted the sea-border of North Chile into a desert and

that of Peru into a region of semi-sterility.

(4) It is considered that this has been effected through the prevailing

winds acquiring drying qualities on crossing the cold waters of the

current in tropical latitudes.

(5) To establish this it is shown that when the Humboldt current leaves

the coast at Cape Blanco mangroves thrive in the Gulf of Guayaquil, and

that when it strikes the coast again near Santa Elena Point and courses

along that seaboard to the equator we find the Peruvian conditions of

semi-sterility reproduced.

(6) The probability that the arid climate of Peru is in our own time

extending northward into Ecuador is pointed out; and from the presence

of old coral blocks on the Peruvian beaches it is considered likely that

when these corals throve the mangroves extended far down the coast of

Peru.

(7) It is shown from the presence of the same species of mangroves on

the Pacific and Atlantic coasts of America that there must have been,

not long ago, a communication between these two oceans across Central

America; but it is at the same time observed that this could not be

inferred from shore-plants with buoyant seeds that, like Entada

scandens, occur inland, since, although they occur on both sides of the

continent, their distribution can be explained by the transport of their

seeds by rivers to the Atlantic and Pacific coasts, such as we see in

operation on the Panama isthmus in our own day.

(8) Stress is laid on the great development of mangroves in the Gulf of

Guayaquil and in the Guayas estuary; and it is pointed out that there

are in this locality two varieties of Rhizophora mangle, a large and a

small variety, the first approaching in some of its characters the

Asiatic species, R. mucronata, and being akin also to the seedless

intermediate form of Fiji.

(9) Amongst other matters dealt with in this chapter are the floating

seed-drift of the Guayas or Guayaquil River and the shore plants and

stranded seed-drift of the Panama isthmus. From the locality last named

we learn that rivers bring down from the interior to the Atlantic and

Pacific coasts much the same seed-drift, and that from this centre

littoral plants with buoyant seeds can be distributed over the whole

tropical zone.

CHAPTER XXXIII

SEED-DISPERSAL AND GEOLOGICAL TIME

The shifting of the source of the Polynesian plants from the New to the

Old World.—The floral history of Polynesia stated in terms of

geological time.—The suspension of the agencies of dispersal in later

periods.—Parallel differentiation in the course of ages of climate,

bird, and plant.—New Zealand.—Insects and bats as agents in

plant-dispersal.—The effective agency of sea-birds in other

regions.—The observations of Ekstam.—The Spitzbergen controversy.—The

efficacy of ducks as distributors of aquatic plants.—Summary.

IN the matter of the dispersal of seeds by birds in the tropical

Pacific, there are at least two questions which my readers must have

frequently put to themselves. The one would be concerned with the

shifting of the source of the Polynesian plants from America to the Old

World, which occurred probably near the close of the Tertiary period.

The other would be connected with the suspension of the work of

dispersal over a large portion of Polynesia, which has become more and

more pronounced as we approach our own day.

_Suggested Cause of the Shifting of the Source of the Polynesian Plants

from the New to the Old World._—In previous chapters we have discussed

the various epochs in the plant-stocking of these islands. There was

first the age of Coniferæ, in which the islands of the Western Pacific

were only concerned, an age prior to the appearance of the volcanic

groups of the Tahitian and Hawaiian regions, and placed in the Secondary

period. Then followed, in the Tertiary period, after the birth of Hawaii

and Tahiti, and when the island-groups of the Western Pacific were

mainly submerged, the general dispersion from America of the Compositæ,

Lobeliaceæ, and other orders, now represented only by genera peculiar to

the Hawaiian and Tahitian islands. Last of all, towards the close of the

Tertiary period, when the island-groups of the Western Pacific had

re-emerged, a general dispersion of Old World plants, mainly Malayan,

took place over all the present archipelagoes of the tropical Pacific.

Since the climate of Hawaii must have, to a great extent, shared in the

vicissitudes of the continental climates of the northern hemisphere

before, during, and after the Glacial epoch, it is assumed that in the

Ice Age no tropical plants reached the group, and that only the plants

now represented in its mountain-flora could have then reached there. The

area of active dispersion of tropical plants was pushed far south.

During the Ice period, Indo-Malayan plants doubtless crowded into the

equatorial region of the Western Pacific; but, cramped and confined

within this limited area, they were cut off by a climatic barrier from

the cool latitudes of Hawaii. As the cold ages passed away, migratory

birds, confined during that period to the southern hemisphere, would

extend their ranges north, sometimes reaching Hawaii, and transporting

to it the seeds of New Zealand and Antarctic genera, now represented by

endemic species on its mountain-slopes. The Indo-Malayan plants, with

the increasing warmth in the climate of the northern hemisphere, would

overrun the Pacific, set free from their prison in the south-west

portion of that ocean. Dispersal, we might imagine, would be at first

very active over the whole ocean.

My point is, then, that whilst the Malayan era of the plant-stocking

began after the Ice Age in the northern hemisphere, the dispersion of

the New Zealand and Antarctic genera over the Pacific took place during

that period; whilst, as before noticed, the dispersion of the Compositæ,

Lobeliaceæ, and other orders, represented now in Hawaii by endemic

genera, would be pre-Glacial and well back in the Tertiary epoch. I

would, therefore, suggest the following scheme, in illustration of the

floral history of the tropical Pacific.

(1) The Age of Conifers of the Western Pacific during the Mesozoic

period, and before the appearance of the Hawaiian and Tahitian

archipelagoes.

(2) The Age of Compositæ and Lobeliaceæ, and of other genera. This is an

era of American plants, and it is referred to the Tertiary period. In it

only the newly-formed Hawaiian and Tahitian groups shared, the islands

of the Western Pacific being largely submerged.

(3) The Age of Malayan plants, regarded as mainly post-Glacial, and

subsequent, therefore, to the re-emergence of the Western Pacific

islands at the close of the Tertiary period.

Dispersion then was general over the Pacific. The distribution of the

New Zealand and Antarctic genera, plants that take a subordinate part in

the floras of the Pacific islands, is regarded as having occurred during

the glaciation of the northern hemisphere.

_On the Suspension of the Agencies of Dispersal in the Tropical

Pacific._—If the remark of Drake del Castillo that genera possessing

only non-endemic species in the Pacific islands owe their presence in

this region to existing agencies of dispersal looks something like a

truism, we must remember that, assuming Nature to be uniform in her

methods, it involves not merely the original co-operation of the same

agencies with genera that own only peculiar species, but also the

subsequent suspension of the work of these agencies.

The nature of the connection between freedom of dispersal and specific

differentiation is well brought out by Beccari in contrasting the

species of Ficus and the palms of Borneo; whilst out of fifty-five

species of Ficus collected by him in that island, 30 per cent. were

apparently peculiar, 85 per cent. of the 130 Borneo palms had not been

found elsewhere. In the English edition of his _Nelle Foreste di Borneo_

he says that “the explanation lies in the fact of the facile

dissemination of the various species of Ficus through the agency of

birds, an explanation which applies to all trees which produce edible

fruits specially relished by animals.” He shows, also, that the same

principle applies within the limits of the genus Ficus, since of those

Bornean species known to him as belonging to the section Urostigma,

which possesses fruits most preferred by birds (pigeons, hornbills,

&c.), nearly all (fourteen out of sixteen) are found elsewhere; whilst

of ten species belonging to the section Covellia, where the fruits are

more or less hidden and inconspicuous, and with difficulty discovered by

birds that would effectively distribute the species, four, at the most,

are found elsewhere. “Such facts,” he goes on to say, “show that in

tropical countries the various kinds of Ficus are, to a large extent,

biologically connected with birds, which, perhaps, on their part, also

owe some of their peculiarities in the shape of the bill or in the

plumage to the nature and coloration of the fruits which form their

food.”

Whilst Dr. Beccari as a botanist lays especial stress on the biological

connection in Malaya between the plant, as illustrated by the genus

Ficus, and the bird, Mr. Perkins, as a zoologist, is similarly emphatic

on the biological connection in Hawaii between the bird, as illustrated

by the peculiar family of the Drepanididæ, and the plant. The plants

here are the arborescent Lobeliaceæ and the Freycinetias. To the flowers

of the arborescent Lobeliaceæ the nectar-feeding Drepanids are

particularly partial; and the development of the extreme forms of these

birds, as Mr. Perkins observes in the _Fauna Hawaiiensis_, “is not

comprehensible without a knowledge of the island flora.” Not only does

he point to the modifications in the form of the bill of the bird in

connection with the tubular form of the flowers; but in at least one

species of these arborescent Lobeliaceæ he shows that it is dependent on

the Drepanid for its fertilisation, and he inclines to the view that

changes such as that of lengthening of the bill may have taken place

side by side with the increasing length of the tubular flowers. In

connection with the Freycinetias of Hawaii, Mr. Perkins regards the bill

of the Ou, a finch-like Drepanid of the genus Psittacirostra, as

“entirely formed and adapted for the purpose of picking out the

component parts” of the fruiting inflorescence.

That in an isolated island-group birds and plants often “differentiate”

together is a fact well known in distribution. In Hawaii, for instance,

as I learn from Mr. Perkins, quite 45 per cent. of the birds are

peculiar; whilst according to Dr. Hillebrand 80 per cent. of the

flowering plants are confined to the group. Then, again, in the

Galapagos Islands, half of the plants and two-thirds of the birds are

confined to that archipelago. At the other end of the series we have the

Azores, with about a tenth of its plants peculiar, and about 4 per cent.

of its birds peculiar to the islands, and Iceland with no endemic plants

and, as far as I can gather, few peculiar birds.

Accepting Mr. Charles Dixon’s view (_The Migration of Birds_, 1897) that

specific differentiation does not occur along lines of migration, we

must assume that the differentiation of the avifauna of an isolated

group like Hawaii began with the breaking off of its regular

communication through birds with the outside world. I do not consider

that in the past these Pacific archipelagoes received their birds in any

haphazard fashion, as, for instance, in the guise of stragglers that had

lost their way. From the circumstance pointed out to me by Mr. Perkins

that 25 of the 67 genera of Hawaiian birds are peculiar, we must

postulate a high antiquity for the bird fauna dating far back into the

Tertiary period. Mr. Perkins, who kindly supplied me with his general

views of the nature of the Hawaiian fauna, tells me that it is

“positively oceanic-insular and could be continental only on the

supposition that everything continental had been at some time destroyed

and that the group had been subsequently re-stocked as would any oceanic

island.”

The view naturally presents itself that in past ages birds in the

Pacific were much more uniform in their characters, and the agencies of

dispersal far more active in their operations and far more general in

their range than in more recent times, “It may be accepted (says Mr.

Dixon) as an axiom of geographical distribution that all existing

species are surviving relics of more ancient forms or ancestral types,

whose dispersal in a remoter past was more continuous, and whose

affinities and characteristics were therefore more homogeneous.” I

assume that in past ages the differentiation of birds has largely been

favoured by differentiation of climate acting through the limitation of

their ranges. To these changes, plants, so often biologically connected

with birds, have largely responded.

There is, of course, no difficulty in imputing to birds the capacity of

reaching Hawaii in the mid-Pacific, and there are many regular migrants

now (sea-birds, waders, ducks, &c.). The only difficulty is in the

estimation of the time occupied in the trans-oceanic journey. According

to Gätke the journey, which is 1,500 to 2,000 miles, ought to be

accomplished within the limit of fifteen hours, which he regards as “the

longest spell during which a bird is able to remain on the wing without

taking sustenance of any kind.” As he considers that a bird might cover

the 1,600 miles between Newfoundland and Ireland in nine hours

(_Heligoland as an Ornithological Observatory_, p. 140), the Hawaiian

traverse would offer to him no difficulties. It has frequently occurred

to me in this connection that in ancient times, when the volcanoes of

the mid-Pacific were in full activity, their light at night-time would

have often given a direction to the migrating bird, and that they might

have sometimes determined the line of migration across the Pacific.

It has not been possible to discuss here the capacity of pigeons to

cross an ocean, a subject bearing directly on the floras of all the

Pacific groups (excepting Hawaii, which possesses no indigenous Columbæ)

and as concerning these islands generally presenting no difficulty. Dr.

H. de Varigny, who amongst his other studies has long displayed an

active interest in plant-dispersal, has directed my attention to two

very important papers on the flight of pigeons in the _Revue

Scientifique_, one by M. A. Thauziès (April 30, 1898) and the other by

M. M. Dusolier (Nov. 28, 1903). That land birds, as well as swimmers and

waders, cross the Atlantic is well known, and in this connection the

reader might profitably consult Prof. Heilprin’s _Geographical

Distribution of Animals_ (vol. 58, _Internat. Sci. Ser._ 1887).

Much might be said of these matters, but it would be out of place here;

and I will content myself with stating the view above indicated that the

suspension of the agencies of seed-dispersal over the Pacific is

probably connected with a general principle affecting the whole

plant-world. The tendency in the course of ages has been towards the

differentiation of climate, bird, and plant, the range of the bird being

largely controlled by the climate, and the range of the plant being

mainly dependent on the range of the bird.

It is evident that in some cases the plants themselves may make the

endemism of a flora more pronounced by creating their own difficulties

and by standing in the way of their own dispersal to outside regions. It

has been shown that some of the endemic Hawaiian genera (see Note 68)

have deteriorated in their capacity for dispersal by birds; and similar

remarks are made with reference to the genera Sicyos (page 365) and

Eugenia (page 350). Genera with stone fruits like Elæocarpus possess in

the different species stones of various sizes, some of them suitable in

point of size for conveyance in a bird’s body over an ocean, others so

large that one could only predicate for them a limited capacity for

distribution by birds over a few hundred miles of sea. One, for

instance, could safely assume that species of Elæocarpus, with stones an

inch and over in size, that occur in Fiji and Hawaii, are not suited for

distribution over an ocean now; whilst other species found in New

Zealand and Rarotonga have stones less than half this size, which are

quite fitted for distribution by birds over broad tracts of ocean (page

337).

This brings us to discuss the relative difficulties presented from the

dispersal-standpoint by the forest floras of Hawaii, Fiji, and New

Zealand. It is with the forest floras that nearly all the difficulties

of distribution lie; and I hope I shall not be considered presumptuous,

or at all events too heterodox, in expressing the opinion that judging

from the details given in Kirk’s _Forest Flora of New Zealand_ those

islands present no greater difficulties for the student of

plant-distribution, if we exclude the Coniferæ, than either Fiji or

Hawaii. Indeed, even with the Conifers included, New Zealand presents

fewer problems than Fiji, and Hawaii has its own special difficulties

connected with the inland species of the Leguminosæ. There is, on the

other hand, no special New Zealand difficulty. It possesses the Conifers

in common with Fiji; and it shares with Fiji and Hawaii genera like

Elæocarpus and Sideroxylon, that take a foremost place amongst the trees

of the Pacific forest flora presenting puzzling points to the student of

distribution. The existence of Elæocarpus in New Zealand admits of a

simpler explanation than the occurrence of the same genus in Hawaii.

Pandanus in Fiji is a more difficult genus from the standpoint of

dispersal than Corynocarpus in New Zealand, and in fact, than any of the

non-coniferous genera of forest trees in that region.

Whilst it is likely that birds of the genus Porphyrio have, up to almost

recent times, been active in distributing the seeds of New Zealand

plants outside the region (see p. 296), it would seem that the

fruit-pigeons, as represented by a solitary peculiar species of

Carpophaga, have long since ceased to be active in this direction. It is

true that Sir W. Buller gives a long list of trees, including

Corynocarpus, Elæocarpus, Litsea, Olea, Podocarpus, and many others, the

fruits of which are appreciated by this pigeon; but since the bird is

confined to this region its efforts in plant-dispersal possess only a

local interest. Mr. G. M. Thomson, indeed, has expressed the opinion

(_Trans. and Proc. N.Z. Instit._ vol. 33) that in recent times not a

single plant has been added through the agency of birds to the New

Zealand flora. Besides the regular migratory birds two cuckoos only

reach the region, the one from Australia and the other from Polynesia;

whilst Australian birds which had managed to survive the long flight

across the ocean have been met with only at times on the west coast of

the North Island. From the standpoint adopted in this work we should

have expected that, with the exception of current-dispersed plants, New

Zealand would be out of touch with the world outside. Varied only by

occasional inrushes of plants, its history, dating back to the Mesozoic

age, has been one of insular isolation.

When, however, we apply the principles of plant-dispersal in the

Pacific, deducible from the study of the Hawaiian flora, we learn that

the stocking of New Zealand with its plants could have been carried out

(with the exception of the Coniferæ and a few other genera like Fagus

that are in a geological sense ancient denizens in this region) by the

agencies that stocked Hawaii with its flora. New Zealand genera like

Elæocarpus, Sideroxylon, Sophora, etc., that are represented in the

forests of Hawaii, could not be taken to illustrate any former

continental connection. If we, so-to-speak, put the New Zealand forest

flora in the Hawaiian sieve, all will pass through with the exception of

Fagus, the genera of the Coniferæ, and plants of similar history in high

southern latitudes. This residuum belongs more to the palæobotanist than

to the student of means of dispersal.

I should be inclined to think that the tropical genera of the New

Zealand flora, more especially of the forest flora, reached that region

during the glaciation of the northern hemisphere, when the Indo-Malayan

plants were, so-to-speak, cornered in the Western Pacific. Yet it must

be noted that these are, as a rule, genera that either display an

indifference to the varying thermal conditions of different latitudes or

are known to at times extend their range beyond the tropics. Thus

Elæocarpus and Freycinetia are equally at home in the temperate

rain-forests of New Zealand and in the tropical rain-forests of

Polynesia and Malaya; whilst widely-spread tropical genera like

Pittosporum and Peperomia, that occur in New Zealand, exhibit their

power of adaptation to varying climates by extending outside the tropics

in other regions and by their vertical range in the Hawaiian mountains,

where they are found alike at low elevations a few hundred feet above

the sea and at altitudes of 6,000 or 7,000 feet.

All these plants, however, are in a relative sense recent intruders.

When the student of dispersal looks at the long list of the conifers of

the New Zealand forest flora and reflects that he knows but little of

their means of dispersal, and that if his acquaintance were far greater

it would not avail him much, he has no choice but to take his place

behind the earlier investigators of the flora, and to see in these trees

evidence in favour of a remote continental period, probably referable to

the mesozoic age.

_A Discussion of some Means of Dispersal._—Not many authors seem to have

discussed the possibility of insects as agents of seed-dispersal in the

Pacific. They appear to me quite suited for transporting the spores of

ferns and lycopods as well as the minute seeds of plants like the

orchids and the begonias. Darwin, who allowed few possible means of

dispersal to escape his notice, procured the germination, as my readers

will remember, of grass seeds found in the dung of Natal locusts. When

on the barren summit of Mauna Loa, I noticed that the recently dead

bodies of some butterflies, that had been carried up the slopes from the

forests below by the “southerly updraught,” were already attacked by

bugs, parasites that must have been transported from the lower regions

by some of the numerous larger insects that are blown up the slopes.

In Note 61 the occurrence of the wind-blown insects on the summit of

Mauna Loa is described. That insects can be transported into the upper

regions of the atmosphere by ascending air-currents was long ago

remarked by Humboldt, and the subject has been discussed with his usual

acumen by Whymper (_Travels amongst the Great Andes of the Equator_).

Carried along in the higher air-currents these insects might finally be

deposited at places far distant from their home. One reads occasionally

extraordinary accounts of a rain of insects. A very circumstantial

account was given to me when I was on Keeling Atoll of a shower of

dragon-flies that fell on the islands, their remains being found in

quantities in the lagoon. Dragon-flies, it is known, are often found at

sea far from land, and one species has been observed nearly all over the

world, including the Pacific islands. In this connection it is

interesting to recall Mr. M’Lachlan’s remark in his article on the

dragon-fly in the seventh volume of the _Encyclopædia Britannica_ that

some of the earliest fossil forms seem to have been washed ashore after

having been drowned at sea.

Another creature that has been often ignored as a possible agent in

seed-dispersal is the bat. Bats are found all over the world, including

the oceanic groups, and one can scarcely doubt that they must have often

transported seeds, at all events in their hair. They are found at times

high up in mountainous regions, and Sir H. Johnston, in his recent work

on the Uganda Protectorate, refers to the occurrence of bats at an

altitude of 13,000 feet. The large frugivorous bats (Pteropidæ) are

known to be very destructive feeders; but I doubt whether they swallow

the seeds. Dr. Warburg, as is remarked in Chapter XXV, says that they

feed on the flowers of Freycinetias, and I have already observed that

they visit the flowers of Geissois ternata in Fiji (p. 394). In this

fashion Dr. Warburg regards them as agents in pollenisation; and it

seems to me that if, as appears likely, they are attracted by trees with

large, brightly-coloured flowers, they would often aid in the dispersal

of the minute seeds of trees like Metrosideros.

Until recently sea-birds, and some particular birds of passage, have

been generally considered as only fitted for dispersing seeds in their

plumage. That they can also transport seeds inside their bodies is shown

below. Dr. R. Brown in his book entitled _Our Earth and its Story_,

1888, gives a general account of plant-dispersal with numerous

references to the Literature on the subject. On the direct route between

Scotland and Cape Farewell in Greenland snow-buntings (Plectrophanes

nivalis) and other birds of passage frequently alight, as we are told,

on ships when hundreds of miles from land. Dr. Brown says that when

taking this voyage he examined dozens of these birds. Only in one case,

however, did he find any seeds, namely, in the case of a snow-bunting

which carried, attached to its plumage, an achene of, perhaps, a

Ranunculus, and in its gizzard a seed like that of a Suæda. My discovery

of a small, hard seed in the gizzard of a Cape-pigeon (Daption capensis)

550 miles east of Tristan da Cunha has been referred to by Mr. Hemsley

in his introduction to the _Botany of the “Challenger” Expedition_ (p.

45). On p. 188 I have mentioned the probable dispersal of the seeds of

Cæsalpinia by frigate-birds and boobies; and in Note 59 reference is

made to some large seeds found in the crop of the Fulmar petrel.

Gulls, when they nest at the coast, where the sea-thrift (Armeria

vulgaris) and the sea-campion (Silene maritima) thrive, or inland

amongst the heather-covered slopes, must often carry the seeds of these

plants from place to place in their plumage (see Notes 15 and 16); but,

as shown below, they can also disperse plants with fleshy fruits which

at times form their food. Gulls, geese, and arctic grouse take an

important part in the dispersal of seeds in the cold latitudes of the

northern hemisphere; and few things are more suggestive in this way to

the student of distribution than the data supplied by Ekstam, Hesselman,

Sernander, and others for the region including Spitzbergen, Nova Zembla,

and Arctic Norway. The history of the discussion relating to the flora

and fauna of Spitzbergen reproduces in its main features the various

stages in the controversy that has been waged in connection with the

Pacific islands.

When Ekstam published, in 1895, the results of his observations on the

plants of Nova Zembla, he observed that he possessed no data to show

whether swimming and wading birds fed on berries; and he attached all

importance to dispersal by winds. On subsequently visiting Spitzbergen

he must have been at first inclined, therefore, to the opinion of

Nathorst, who, having found only a solitary species of bird (a

snow-sparrow) in that region, naturally concluded that birds had been of

no importance as agents in the plant-stocking. However, Ekstam’s

opportunities were greater, and he tells us that in the craws of six

specimens of Lagopus hyperboreus shot in Spitzbergen in August he found

represented almost 25 per cent. of the usual phanerogamic flora of that

region, in the form of fruits, seeds, bulbils, flower-buds, leaf-buds,

&c. This observer now also realised the importance of gulls and geese in

dispersing certain types of plants in those latitudes. Species of Larus,

he says, consume greedily all kinds of berries, and especially those of

Empetrum nigrum, the stones of which were found uninjured in their

droppings by Professor Lagerheim in Arctic Norway. Geese, as we are also

informed, are hearty plant-eaters in Spitzbergen; and Ekstam found in

their droppings the fruits of Oxyria digyna as well as an abundance of

uninjured bulbils of Polygonum viviparum, some of which proved to be

capable of growth (See Ekstam in _Tromso Museums Aarshefter_, vols. 18

and 20, 1895-7).

The result of Ekstam’s observations in Spitzbergen was to lead him to

attach a very considerable importance in plant-dispersal to the agency

of birds; and when in explanation of the Scandinavian elements in the

Spitzbergen flora he had to choose between a former land connection and

the agency of birds, he preferred the bird.

I have gone into some detail in this matter because the Spitzbergen

controversy in some respects might have equally centred around New

Zealand or some of the large continental islands of the tropical

Pacific. There is at first the endeavour in the absence of precise

knowledge to disregard the bird and to look for a land connection. With

the increase in our acquaintance with the efficacy of bird-agency in

seed distribution there is the abandonment of such a view. In both

localities, however, there are the same counter-indications of the

insect faunas, and the same considerations are raised by the absence or

presence of larger animals in the regions concerned. The principal

difference lies in the frozen sea, and yet, strangely enough, it does

not seem to affect the problem much. It would indeed appear that the

questions raised by the floras and faunas of the Pacific islands are not

peculiarly Pacific in their character; and it is probable that the

difficulties here presented are repeated in one form or other in the

case of large islands over all the globe.

_On the efficacy of Ducks and other Waterfowl in the Distribution of

Aquatic Plants._—It is highly probable that aquatic plants, like the

beach plants distributed by the currents and the ferns and lycopods

distributed mainly by the winds, have changed much less in the course of

ages than the plants of the inland forest. This in all three cases is

chiefly due to the uninterrupted freedom of communication by means of

the dispersing agency.

Wild ducks and their kind are active agents in the distribution of the

seeds of aquatic plants; but it is curious that the early experiments of

Caspary went far to discredit them in this respect. As quoted by Dr.

Schenck in his _Die Biologie der Wassergewächse_, 1886, he fed tame

ducks with the seeds of water-lilies and found that in a short time they

thoroughly digested the seeds. Those familiar with the seeds of our

British species of Nuphar and Nymphæa will not be surprised at such a

result; but, unfortunately, the inference drawn from this experiment has

been by some extended to aquatic plants in general. Since the seeds or

seed-vessels of some aquatic or semi-aquatic plants of the genera

Potamogeton, Sparganium, &c., appeared to me to be quite fitted for

conveyance without injury in a duck’s body, I made several years ago a

number of observations on this subject, the results of which were

published in _Science Gossip_ for September, 1894.

Out of 13 wild ducks obtained in the London market and stated to have

been sent from Norfolk and Holland, eleven contained in their stomach

and intestines 828 seeds, which I thus classed:—

295 seeds of Sparganium in 8 birds

41 seeds of Potamogeton in 3 birds

270 seeds of Cyperaceæ in 5 birds

222 not identified