One can imperfectly distinguish two sets_Observations of a Naturalist in the Pacific Between 1896 and 1899, Volume 2 Plant-Dispersal

the first comprising such plants as Pachyrrhizus trilobus, Tacca

pinnatifida, Amorphophallus campanulatus, the Mountain Bananas, the Wild

Yams, and several others that grow wild, and, as a rule, only serve as

food in times of scarcity; the second including the plants that are

extensively cultivated by the present islanders, such as the Breadfruit,

the Banana (Musa paradisiaca), the Taro (Colocasia antiquorum) and the

two Yams (Dioscorea alata and D. sativa), &c. Those of the first set

probably formed the food of the earliest inhabitants of the Pacific

Islands, pre-Polynesian peoples that practised only a rude sort of

cultivation, as with the present “bush-men” of the islands of the

Western Pacific. Those of the second set belong to the later occupants

of these islands, the Polynesians.

(a) _The Pre-Polynesian food-plants._—In addition to those above named

one may mention Cycas circinalis, Cyrtosperma edulis, Lablab vulgaris,

Pandanus odoratissimus, Saccharum officinarum, Sagus vitiensis, &c.

Inocarpus edulis is probably to be here included, and amongst the Wild

Yams should be named Dioscorea nummularia and D. pentaphylla. Some of

them are now occasionally cultivated; but most of them only occur in the

wild condition, either as weeds or as larger plants growing

spontaneously in uncultivated localities. Even the knowledge of them as

food-plants has sometimes been altogether lost, the present inhabitants

of the Fijis, for instance, knowing nothing of Lablab vulgaris and Sagus

vitiensis as sources of food. The question of the antiquity of the

Coco-nut Palm in Polynesia was discussed at length by Seemann; but for

various reasons we cannot be absolutely certain whether or not it is an

older denizen of the Pacific islands than the Polynesian. It is,

however, to be inferred that it came originally from the home of the

genus in America, perhaps as a gift brought by the Equatorial Current

from the New World to Asia. Several chapters might be devoted to the

discussion of the earlier food-plants of these islanders; but here only

a brief reference can be made to a few of them.

Perhaps the oldest of the earliest aboriginal food-plants are those

that, like Cyrtosperma edulis and Sagus vitiensis, are apparently

confined to Fiji. Here we seem to possess indications of the development

of new species since that group was first occupied by man. Others, like

Pachyrrhizus trilobus and Cycas circinalis, that are restricted to the

groups of the Western Pacific may come next in relative antiquity.

Although most of the early food-plants hail from the Old World, the home

of Pachyrrhizus is in America. One may indeed wonder how a plant with

such a history ever reached the Western Pacific. It seems to be

generally distributed in this part of the ocean, having been recorded

from New Caledonia, the New Hebrides, Fiji, Tonga, and Samoa. Although

its edible roots are only used in times of scarcity, the plant grows

wild all over Fiji, being especially frequent in the “talasinga” plains.

Though I searched diligently, it never presented me with its seed. In

Tonga, according to Graeffe (as quoted by Reinecke) the plant is much

employed in preparing the land for yam-cultivation, since it restrains

the growth of weeds and keeps the soil moist.

Amongst the food-plants of this early period that are distributed over

the South Pacific as far east as Tahiti may be mentioned the Wild Yams

(D. nummularia and D. pentaphylla), the Mountain Bananas, Tacca

pinnatifida, Amorphophallus campanulatus, and others. Of these Tacca

pinnatifida and Dioscorea pentaphylla are alone found in Hawaii. I will

only now refer to the Mountain Bananas.

The Mountain Bananas of the tropical South Pacific, distinguished by

their erect fruit bunches and their seeded fruits, present us with one

of the mysteries connected with aboriginal man in this ocean. Whether in

New Caledonia, Fiji, Samoa, Rarotonga, or in Tahiti, they grow wild in

the interior, and form often a conspicuous feature of the vegetation in

the mountains and at the heads of the valleys. They are occasionally

cultivated. Their Fijian and Samoan names of “Soanga” and “Soa’a”

reproduce the names of the banana, “Saguing” and “Saing” in the Tagalog

language of the Philippine Islands. The Tahitian appellation is “Fehi”

or “Fei,” and this reappears in Samoa in the form of “Fa’i,” the word

for the common cultivated banana, Musa paradisiaca. The Rarotongan name

of “Uatu,” as given by Cheeseman, is suggestive of the Micronesian form

(Ut, Uut, &c., in the Carolines) of a widely spread banana word in

Malaya, Melanesia, and West Polynesia (Fudi, Vundi, Undi, &c., &c.). It

is not unlikely that all these South Pacific mountain bananas with erect

inflorescences and seeded fruits belong to one species, variously

designated by botanists as Musa fehi, M. uranoscopus, M. troglodytarum,

&c., and confined to this region. Under the name of Musa fehi Schumann

includes the New Caledonian and Tahitian plants, and he views the Samoan

plant as probably identical with them. This botanist, in his monograph

on the Musaceæ (Engler’s _Das Pflanzenreich_, 1900), establishes the

home of the bananas in tropical Asia, and considers that their

occurrence in America before the time of Columbus has not been proved.

Birds have no doubt often assisted in the dispersal of the wild, seeded

plants; but it is likely that man is responsible for the occurrence of

the mountain forms in the Pacific, and probably their fruits formed when

cooked one of the principal articles of diet of the earliest immigrants.

(There evidently exists in Vanua Levu a plant very like the African Musa

Ensete. Its presence was only indicated by the occurrence of its empty

seeds in the stranded beach-drift, and reference is made to it in that

connection in Chapter XXIX.)

(b) _The Polynesian food-plants._—The cultivation of the yams, the

taros, the breadfruits, and the bananas in later ages all over the

Pacific islands cannot here be dealt with. My readers will already know

that a very ancient cultivation is in each case indicated by the

occurrence of a great number of varieties. Much has been written upon

this matter, and amongst the recent contributions to the subject may be

reckoned Mr. Cheeseman’s interesting paper published in the

_Transactions and Proceedings of the New Zealand Institute_ (vol.

xxxiii).

I may here mention in connection with the Sweet Potato (Batatas edulis),

a plant that may have an American origin, though much mystery surrounds

its home, that it rarely seeds in Fiji except when it is grown in poor,

sandy soil, and in dry, rocky situations. The Fijians were quite

incredulous as to its maturing seed; but after much searching I found a

solitary plant in seed and removed their doubts.

THE POLYNESIAN WEEDS

Some curious questions are raised in connection with the weeds of this

region. Polynesia, says Dr. Seemann, presents a most interesting problem

with regard to its weeds. It is, however, necessary to point out that

these plants arrange themselves into two groups, the aboriginal weeds

comprising those existing in the islands at the time of Captain Cook’s

expeditions in the latter half of the eighteenth century, and the white

man’s weeds that have been since introduced.

As concerning the Fijian Islands, Dr. Seemann remarked that although the

majority of the non-endemic plants of the flora is Asiatic, “the bulk of

the weeds is of American origin, or, at all events, is now found in

America.” His principal point was to show that American weeds displayed

a greater disposition than Asiatic weeds to spread in Fiji, because Fiji

was to American plants altogether virgin ground. This is a purely

botanical matter, and we are not in a position to oppose a conclusion

formed by such a careful observer of plant life. But to the ethnologist

it is a very different matter whether most of the Fijian weeds are of

American origin or merely now exist in America. His interest lies

entirely in the aboriginal weeds. To the student of plant-dispersal this

distinction is also a very important one; and his interest again is all

on the side of the aboriginal weeds.

Dr. Seemann enumerates 64 Fijian weeds, of which at least 37 were in the

Pacific islands when Captain Cook’s botanists made their collections

(see Note 82). Of these 22 occur in continental regions on both sides of

the Pacific, 13 are natives of the Old World alone, and two only are

seemingly American exclusively, namely, Waltheria americana and Teucrium

inflatum. The first is claimed to be American because most species of

the genus are American, but it is now widely distributed in the Old

World as well as in America. The second, though widely distributed in

tropical America, has strangely enough only been found in the islands of

the Western Pacific.

The important point is thus brought out that although in Captain Cook’s

time the food-plants cultivated by the Polynesians, such as the banana,

the breadfruit, the taro, and the yams, were almost exclusively Asiatic

in origin and bore Malayan names, a large proportion of the weeds were

not exclusively Asiatic, but occurred in America as well as in the Old

World. The inference to be drawn, however, is not, as Dr. Seemann

implies, that the Polynesians derived several of their weeds from

America (since with few exceptions all the aboriginal weeds named in

Note 82 occur in the Old World, and in more than a third of the plants

in the Old World only), but that many so-called cosmopolitan weeds were

distributed very much as they are now, when the Polynesians brought

their food plants from Indo-Malaya into the Pacific.

Weeds follow the cultivator in all climates; and it is very natural

that, as Mr. Hemsley points out, plants which seem to owe their wide

dispersal to cultivation are not found in Australia (_Bot. Chall.

Exped._, iii, 142). The Australian native as a rule cultivates nothing.

Yet I fancy that man’s share in weed dispersal is as often as not merely

restricted to producing the conditions favourable to the growth of

weeds, and that the seeds are often brought by birds and other agencies.

Many weeds of the genera Atriplex, Polygonum, and Ranunculus are

dispersed by partridges in England, and I have often found the uninjured

fruits of the plants in the stomachs of these birds. Many weeds, like

Prunella vulgaris, Plantago major, Capsella bursa-pastoris, Luzula

campestris, and several others named in Note 43, possess seeds or fruits

that become “sticky” when wet, and would readily adhere to a bird’s

plumage.

We can also say of tropical weeds that many of them are distributed by

birds. In the crop of a dove in Hawaii I found a number of the small dry

fruits of Waltheria americana, the widely spread tropical weed before

mentioned, and of another weed of the order Compositæ. On the bare rocky

peak of one of the Vanua Levu mountains the only plants found growing

were Oxalis corniculata and a species of Peperomia, both of them

evidently growing from seed dropped by birds. The fruits of Urena lobata

and of species of Sida, as well as those of Bidens pilosa and Ageratum

conyzoides, could be readily dispersed, entangled by their appendages in

the plumage of birds, whilst the sticky achenes of Adenostemma viscosum

would easily adhere to feathers. Weeds with drupes or berries like

Geophila reniformis and Solanum oleraceum would attract frugivorous

birds, and I have often seen berries of the last-named pecked by birds.

Man has doubtless often been the agent in dispersing the seeds of

Leguminous weeds like Lablab vulgaris. On the other hand, we know from

the observations of Focke (see page 150) that birds can distribute the

seeds of a plant like Vicia faba; and in the Pacific islands it is

evident from the frequent occurrence of Tephrosia piscatoria on bare

rocky hill tops that its seeds are dispersed through the same agency.

Birds also probably carry about the seeds of Cardiospermum halicacabum.

If we based our conclusion solely on the distribution of weeds without a

previous study of their means of dispersal we might, as students of the

distribution of man, acquire some startling and very erroneous notions

on the history of the races of man, especially in the New World. Lacking

such an acquaintance with existing modes of dispersal it would not be

prudent to attach too much importance to the occurrence of Asiatic weeds

in America and of American weeds in Asia. Mr. Hemsley, in his work on

the botany of Central America (_Biologia Centrali-Americana_), gives a

list of ten British plants of world-wide range, which we will designate

plants of waste places rather than weeds. They are plants often found

not only in the Old and New Worlds, but also in the southern hemisphere,

and I will here name them: Radiola millegrana, Alchemilla vulgaris,

Cotyledon umbilicus, Lythrum salicaria, Convolvulus sepium, Sibthorpia

europæa, Prunella vulgaris, Lycopus europæus, Aira cæspitosa, Luzula

campestris. According to this authority these plants “are most unlikely

to have been aided, intentionally or unintentionally, by man” and

“possess no special means of dispersion by animals or birds or the

elements” in the way, as is implied, of appendages like hooks, hairs, a

pappus, &c.

Five of these plants are referred to in various connections already in

this work. In all I have tested the means of dispersal of six or seven

of them; and although my results are not always conclusive, I venture

here to indicate some of them. The nutlets of Prunella vulgaris and the

seeds of Luzula campestris emit mucus when wetted and adhere firmly to

feathers on drying, whilst the nutlets of Lycopus europæus are sticky in

the dry state and adhere to the fingers on handling. This last-named

plant is occasionally to be noticed on rubbish heaps growing with other

waste-plants. No such adhesive qualities, whether in the wet or dry

condition, came under my notice with Alchemilla arvensis or with Lythrum

salicaria. With Alchemilla the seed-like fruits fall from the plant,

inclosed in the dried-up calyx. The seeds of Cotyledon umbilicus are so

minute (1/3 mm. or 1/75 inch) that they can be compared with Juncus

seeds from the standpoint of dispersal. They are naturally a little

sticky and tend to adhere to feathers, but more probably they are

transported in adherent soil. The case of Convolvulus sepium is a very

remarkable one, and I have referred to it on page 29 and in the notes

there indicated. The species of Radiola, Sibthorpia, and Aira have not

been tested by me. Dispersion, however, would be favoured by the small

size of the seeds in the first two species and by the awned glumes in

the case of Aira.

The distribution of aboriginal weeds might be expected by some to supply

data of profound interest to the student of the races of mankind; and I

think the botanist rarely realises how often he tantalises the

ethnologist by the remark that certain weeds have been spread by

cultivation all round the tropics. De Candolle many years ago, in his

_Géographie Botanique_, gave a list of nearly 100 plants, made up of Old

World species naturalised in America and of American species naturalised

in the Old World, and quite half of them were classed as plants

distributed in one way or another through man’s agency. Now this is

either a subject of supreme importance or it is of no interest to the

student of man’s history. If it should prove that birds have done most

of this dispersal, then the story of the aboriginal weed would be of

little interest in connection with the races of man in the New World.

I will now refer briefly from the standpoint of dispersal to a few

interesting Polynesian plants in which man has been in most cases more

or less concerned in their distribution.

ALEURITES MOLUCCANA (THE CANDLE-NUT TREE)

Much interest is attached to this tree, which is found in India, Malaya,

and North-east Australia, and occurs all over the Pacific, extending

north to Hawaii, south to the Kermadec Islands, and east to Tahiti and

Pitcairn Island (Maiden). In the Hawaiian Islands it is often so

frequent as to form whole forests, or at all events to give a character

to the forest zone up to 2,000 feet above the sea. Its prevalence in

Hawaii might be regarded as evidence of its indigenous character; but

its predominance there is due to the circumstance that it is one of the

few forest-trees that the cattle and other animals avoid, most other

trees falling victim to their depredations by the loss of the bark. In

Fiji, though frequent in places, it does not form such a conspicuous

feature in the vegetation as in Hawaii. In Samoa it is abundant in the

coast-bush. In Rarotonga it forms with Hibiscus tiliaceus, as we learn

from Cheeseman, the major portion of the lower forests, a circumstance

which seems to indicate, since both these trees were probably introduced

by the natives, that this island like Hawaii has lost or is losing many

of its original forest-trees. In Tahiti, according to Nadeaud, it is

common from the sea-level up to 3,000 feet above the sea.

As a Polynesian tree, Aleurites moluccana presents itself to me as an

intruder which has often taken the place of trees of the primeval

forests of these islands. That the natives usually employ the oily seeds

for illuminating purposes is well known; and its prevailing name of

Tuitui (Kukui in Hawaii) is derived from the Polynesian custom of

threading the seeds before using them for lighting purposes. One of the

Fijian names, “Sikethi,” is suggestive of “Saketa,” a name for the tree

in the Ternate dialect of the Indian Archipelago. To the modes of

dispersal of this tree, I have devoted much attention.

The more or less empty seeds of this tree are to be commonly found

floating in rivers and stranded on beaches. I have found them in numbers

on the beaches of Fiji and Hawaii in the Pacific, and of the south coast

of Java and of Keeling Atoll in the Indian Ocean. In all I have examined

many hundreds of these seeds, whether stranded on the beaches in the

localities above named, or floating in the Fijian rivers and at sea

amongst the islands of that archipelago. The seeds were always either

empty or contained a kernel in an advanced stage of decay. A sound seed

has no floating power under any condition; and sound seeds are only to

be found in beach drift near the mouths of estuaries, where they have

been freed by the decay of the fruits brought down by the rivers. During

some dredging operations in the harbour at Honolulu several years ago,

quantities of old Aleurites fruits and seeds were brought up. It is only

by means of the floating fruit that the sound seed can be carried any

distance by the currents; but even in this case the opportunities of

wide dispersal are very limited. If one places in sea-water a number of

well-dried fruits, most of them will sink within a week, and all will be

at the bottom in a fortnight.

The seeds stranded on a beach are often found cracked. This I think

arises from long exposure to the scorching rays of the sun. On account

of the hardness of the shell it is very difficult to obtain the kernel

entire; but the Mangaians get over this difficulty, as we learn from the

Rev. Wyatt Gill, by slightly baking the seeds; whilst the Fijians,

according to Mr. Horne, effect the same object by throwing the heated

seeds into cold water. On one occasion I placed an empty seed on a tin

plate kept at a temperature 115° to 120° F., a temperature near that

which the seed would acquire when lying exposed to the sun on a tropical

beach. After five days I found it had reproduced the cracks noticed in

another empty seed from the Keeling beach.

Facts are not wanting with regard to the dispersal of the seeds by

birds; but since the kernel alone is sought for by birds, and as there

is no means of cracking the shell in their stomachs, such an agency is

only available for local distribution. The Messrs. Layard inform us that

in New Caledonia a small crow (Physocorax moneduloides) and a parrot

(Nymphicus cornutus) are very partial to these seeds (_Ibis_, 1882).

They were told that the crow cracked them by carrying them to a

considerable height and letting them fall on a stone. We are not told

how the parrot cracks the seed, which has a shell so hard that the

Malays, I may remark, term the seed “bua kras,” or “the hard seed,”

whilst a hammer is required to break it. However, since Indian parrots,

according to Mr. J. Scott, are able to split open with their beaks the

hard beans of Adenanthera pavonina (_More Letters of Charles Darwin_,

ii, 349), they evidently possess ingenuity in seed-cracking.

My general conclusion with reference to this tree in Polynesia is that

it could not have been distributed, except locally, by birds and

currents; and that it owes its dispersion there principally to man. A

contrary indication seems to be offered by the occurrence of the tree in

the uninhabited Kermadec group; but since Cordyline terminalis also

exists there, a cultivated plant widely dispersed by the Polynesians, it

would appear that these islanders have formerly visited the group. It is

also contended by Canon Walsh that the Cordyline of the Maoris was

introduced into New Zealand by that race. (See Cheeseman in vols. xx and

xxxiii, _Trans. N.Z. Inst._, for papers on the Kermadec flora and on the

food-plants of the Polynesians.)

INOCARPUS EDULIS (THE TAHITIAN CHESTNUT)

Like Aleurites moluccana this tree presents a _primâ facie_ case for

dispersal by currents. As the result of inquiries in this direction I

have formed the opinion, however, that it has been mainly distributed by

man. Though occurring in all the South Pacific groups, as far east as

Tahiti and the Marquesas, it does not occur in Hawaii. With its home in

Malaya it possesses a range closely resembling that of the breadfruit

tree; and yet, although its fruits are often a common article of food in

Polynesia, it requires no cultivation, and reproduces itself so

abundantly in favourable situations that, as Dr. Seemann observes, only

the dense shade of the parents checks the occupation by the seedlings of

all the adjacent ground. It possesses in the Pacific two sets of names,

neither of which I have been able to identify with any Malayan names,

and both occur over much of the region. Thus the Fijian “Ivi” and the

Samoan and Tongan “Ifi” are represented by “Ii” in Rarotonga, “Ihi” in

Tahiti and the Marquesas, “Hi” in Ualan in the Carolines, “Ifi” in

Futuna in the New Hebrides, and “If” in a New Guinea dialect. Then we

have the Tahitian “Mape,” the “Marap” of Ponape in the Carolines, and

the “Mamape” of Fate in the New Hebrides, besides other forms found in

Melanesia.

In the South Pacific islands, as in Fiji, Samoa, Rarotonga, and in the

Tahitian group, it flourishes in low, moist localities at and near the

coast, by the side of streams and estuaries, and in the rich soil of the

lower valleys. In the Rewa delta in Fiji it is especially abundant,

often bordering the creeks in the mangrove swamps, and occupying

stations that are under water when the river is in flood. It may extend

inland in the various groups, but it is in the low-lying, moist, coast

regions that it mostly thrives; and in Fiji it presented itself to me as

essentially a tree of the estuaries, a station strongly suggestive of

dispersal by currents. Schimper, it may be remarked, includes it amongst

the shore vegetation of the Indian Archipelago.

When in Fiji I paid especial attention to the dispersal by currents of

these large fruits, the agency of birds being, of course, negatived by

their size. They are to be commonly observed floating in the rivers when

in flood, as well as at sea between the islands, and stranded on the

beaches. Of those found afloat in the Rewa River not more than a fourth

had a sound seed. Of those stranded on the beaches two-fifths were

empty, two-fifths displayed a rotten seed, and one-fifth had sound

seeds. Of those picked up at sea all were empty. These fruits, unlike

many others in the drift of the Fijian rivers, do not germinate afloat.

They soon lose in the water their outer, fleshy, non-buoyant coat;

whilst the inner fibrous coat, to which the floating power of the fruit

is due, the seed having no buoyancy, is not water-tight, and moisture

soon enters and leads to the decay of the seed. In order to test their

floating power, I placed in sea-water ten mature fruits. Five of them

floated after forty-five days, having then lost most of the outer,

fleshy coat. Two were afloat after sixty days, but their seeds were

rotting. One fruit that sank after five weeks had a sound seed. Most of

them were sown out afterwards in a place where the trees were thriving,

but none germinated, and of two or three examined all had a decaying

seed. The empty fruits may float a long time after the decay of the

seed. Forty days would probably be the extreme limit for the flotation

in sea-water of a fruit with a seemingly sound seed, though a very small

proportion would reach this limit, and I much doubt whether such a fruit

would germinate afterwards.

I, therefore, inferred that currents are only available for the local

dispersion of the fruits of Inocarpus edulis. It is to man that the tree

owes its existence in Tahiti and other groups of the open Pacific; and

it is to be concluded that the occurrence of this tree on Christmas

Island in the Indian Ocean marks an early Malayan occupation of the

island.

GYROCARPUS JACQUINI

The cosmopolitan distribution of this seemingly useless tree, growing,

as Hemsley remarks, in maritime districts throughout the tropics, in

America, Australia, Asia, and Africa, presents one of the puzzles of

plant-distribution. It is by no means universally spread in the Pacific

islands, and I find reference to it only in Fiji and Tahiti. Seemann

says that in Fiji it is common on the beaches of Taviuni and other

islands. I found it to be a rare coast tree on Vanua Levu. It does not

seem to have been recorded by the botanists of the 18th century in the

Pacific. It, however, has evidently been long established there. Nadeaud

does not speak of its littoral station in Tahiti, and says that it grows

best in the regions of the interior up to elevations of 2,000 feet,

where it attains a great size; and its abundance is implied by his

remark that he had to fell many trees to collect the fruits.

The singular fruit, which has two long wings and looks like a

shuttlecock, dries up on the tree; and in course of time it is detached

and falls to the ground. The falling fruit in its descent twists round

like a screw, and hence the Fijians call the tree the Wiri-Wiri tree,

the same name in the form of Wili-Wili being given for a similar reason

to Erythrina monosperma in Hawaii. Schimper (p. 157) truly remarks that

the fruits are too heavy to be carried by the wind across a wide extent

of sea; and I ascertained by experiment that in an ordinary trade-breeze

they would only be carried a few paces. Birds are quite out of the

question as agents of their transport to oceanic islands. We are driven

then either to the agency of man or to that of the current. The trees

grow rapidly and the timber is soft and perishable. The fruits are not

edible, and as far as I could ascertain the tree is of little or no

value to the Pacific Islander, there being at all events no reason to

believe that he has distributed it.

We appeal lastly to the currents, the agency which Mr. Bentham selected

on _a priori_ grounds (Presidential address, _Linnean Society_, 1869).

My experiments in Fiji showed that the fruits, when dried on the tree

and afterwards detached, are able to float over long distances in

sea-water. After two months they were still afloat, the seeds inside

being dry and unharmed. The fruit’s buoyancy was tested in different

conditions, either without the wings, or with both wings, or with but

one wing, and it was found that the wings, which float for only a day or

two by themselves, lessen the buoyancy of the fruit. Of fruits with both

wings attached forty per cent. floated after two months, whilst of those

deprived of the wings all floated after two months. In the ordinary

course of flotation the wings in most cases break off during the first

few weeks, and in the rough-and-tumble of current-transport this would

occur sooner, so that the floating power of most of the fruits would not

be much affected. The cause of the buoyancy in a structural sense

belongs to the Convolvulaceous type. The kernel has no buoyancy, but it

incompletely fills the cavity of the seed-vessel, the coats of which are

quite waterproof, but have no independent floating power.

It is thus evident that like many other shore-trees Gyrocarpus Jacquini

is distributed by the currents. It is not unlikely that its present

sporadic occurrence in the Pacific islands may be due to the gradual

extinction of the tree in this region, either on account of some insect

pest introduced since Cook’s time or from the use of the timber for

fire-wood by the aborigines.

SERIANTHES MYRIADENIA

This is a striking looking Acacia-like tree that might have been fitly

discussed in the chapter on the enigmas of the Leguminosæ. Only four or

five species are named in the _Index Kewensis_, of which one occurs in

Malacca and in the Philippines, a second in New Caledonia, a third in

Fiji, and the fourth, S. myriadenia, over the South Pacific groups of

Fiji, Tonga, and Tahiti. Reinecke does not include the genus in the

Samoan flora; and it is merely assigned to that group by Seemann on the

authority of Mr. Pritchard, the British Consul in Fiji. Though common in

the forests of the larger islands of Fiji, S. myriadenia is most at home

on the banks of the estuaries, usually behind the mangrove belt, but not

beyond tidal influence. The peculiar species, S. vitiensis, I found on

the banks of the estuary of the Mbua River in Vanua Levu, the locality

from which Gray described it. According to the French botanists, S.

myriadenia, in Tahiti, ranges from near the sea to an elevation of 800

metres. The Fijian name of the trees is “Vaivai,” the name also of

Leucæna Forsteri, and of some other introduced trees of the Acacia

habit. The Tahitians apply the same name in the form of “Faifai” to S.

myriadenia.

The Fijians value the trees on account of the wood; but unless the

Polynesians were in the habit of transporting the seeds of their

numerous timber trees, which is most unlikely, it seems at first sight

useless to look to man’s agency for an explanation of the wide dispersal

of a tree like S. myriadenia in the South Pacific. The tough, woody,

indehiscent pods, from 3-1/2 to 4 inches long, floated in my sea-water

experiments in the case of both S. myriadenia and S. vitiensis between

seven and twenty-five days, after drying for some months. The seeds,

about two-thirds of an inch (17 mm.) in length, are only freed by the

decay of the fallen pod, and have no buoyancy. The agency of birds is

evidently excluded; and it is, therefore, to the currents that we must

make our final appeal; but their powers of dispersing the species appear

quite insufficient to explain the occurrence of these trees in Tahiti.

Perhaps, as in the case of Calophyllum spectabile, another Polynesian

timber-tree found in Tahiti (see p. 136), man and the currents have

worked together.

LEUCÆNA FORSTERI

This bush of the Mimoseæ frequents maritime sands in the South Pacific,

and is confined to this region. It has been found in New Caledonia,

Fiji, Tonga, Rarotonga, and Tahiti. The seeds sink and the pods dehisce

on the plant, so that the agency of currents, unless we invoke the

intervention of the drifting log, bearing the seeds in its crevices,

seems to be excluded. Sea-birds might carry the seeds unharmed in their

stomachs, but there is no evidence bearing on birds as agents in the

dispersal of the species. Since the plant has not been recorded from

localities outside the Pacific islands, and since it was collected by

Cook’s botanists in Tonga and Tahiti, it cannot be placed amongst plants

of recent introduction. Although growing on maritime sands in Fiji,

Rarotonga, and Tahiti, it may grow inland, and according to Cheeseman is

particularly abundant in Rarotonga. In Fiji it is apt to occupy

newly-formed alluvial land at the mouth of the rivers, as in the case of

the Rewa; but the “how and why” caused me much fruitless speculation,

and I abandoned the plant in despair. The Fijians sometimes give it the

native name of Serianthes myriadenia, which they then term “Vaivai ni

Viti,” or the Fijian Vaivai. In Tahiti it is named “Toroire,” and in

Tonga “Toromiro.”

MUSSÆNDA FRONDOSA

Mussænda frondosa is the only one of the sixty species of this tropical

Asiatic and African genus that extends into Polynesia. This beautiful

shrub, which is easily recognised by its conspicuous white, leaf-like

calyx lobe, is common everywhere in Fiji, decorating, as Horne fitly

remarks, in the contrast presented by its golden flowers, its large

white calyx leaf, and its green foliage, many an acre of waste, grassy

land, where the orange-coloured doves and the red and the green parrots

flit to and fro. With its home in India, China, and Malaya, it ranges

all over the South Pacific, from the Solomon Islands to Tahiti. Its

berries contain an abundance of small, minutely-pitted seeds, 0·7 mm. or

1/35 of an inch in size, and weighing when well dried about 600 to the

grain. The seeds retain after years of drying the property of clinging

to passing objects by means of a few microscopic, thread-like fibres,

that are attached to their surfaces. In this manner they will fasten

themselves to the point of a knife, and the observer is astonished to

see them dangling in the air from a pin’s point. I suppose that this is

connected with some hygroscopic quality. At all events, it would enable

these light seeds to be carried about not only by birds and bats but

also by insects. It is possible that man has aided in the dispersal of

this interesting plant; but birds, bats, and insects have, I think,

mainly done the work.

LUFFA INSULARUM

This is regarded as a maritime form of Luffa cylindrica, a plant

commonly cultivated throughout the tropics. The South Pacific plant,

which occurs also in Australia and Malaya, has been found in New

Caledonia, Fiji, Tonga, Rarotonga, and Tahiti. In Fiji it grows chiefly

on the “talasinga” plains and in places once under cultivation. I

noticed it in one locality climbing over the branches of an Inocarpus

tree on the banks of the Rewa. In Rarotonga it is common in the lower

regions. It is, according to Nadeaud, fairly frequent on the shore and

in the lower valleys of Tahiti, where it was collected by Banks and

Solander, the companions of Cook. The Pacific islanders, as far as can

be gathered, make little or no use of the plant; and unless it was

introduced accidentally with their cultivated plants, they could

scarcely have been concerned in its dispersal.

In Fiji I made a special point of investigating the mode of dispersal of

this plant. The fruits, which ultimately become dry and fibrous, are to

be seen hanging vertically from the plant as it climbs among the

branches of a tree. The apical disk usually falls off, and many of the

seeds drop out through the hole thus produced; but a few remain

entangled in the fibrous material occupying the interior of the fruit. I

have noticed such fruits floating down the stream of the Rewa River; but

my experiments showed that they do not float more than a week, whether

in fresh or salt water. The seeds, however, possess a hard, impervious

shell, and are well adapted to withstand unharmed prolonged immersion in

the sea. They will evidently float for months. Out of one hundred

selected seeds placed in sea-water, sixty were found afloat and sound

after two months. The cause of the seed-buoyancy is purely mechanical.

Neither the shell nor the kernel has any floating power, the buoyancy

arising, as with Convolvulaceous seeds, from the unfilled space in the

seed-cavity. When in Fiji, I tested the seeds of the ordinary cultivated

tropical form of the plant which had been introduced into a garden from

Australia. They all sank in a few days, and on being cut across the seed

displayed but little unoccupied space in its cavity. I have no doubt

that the Pacific form of this plant has been at times dispersed by the

currents, not, however, through the fruits, but through the seeds. It is

also quite possible that it may have been introduced by a pre-Polynesian

people into the Pacific.

_Summary of the Chapter_

(1) Man in his distribution over the Pacific islands reproduces, but in

a less degree, nearly all the difficulties presented by the plant in its

dispersal. In both we have the age of general dispersion followed by a

suspension more or less complete of the migrating movements; and in both

we have differentiation associated with the isolation.

(2) The Pacific islanders possess two sets of food-plants. In addition

to those commonly cultivated in our own time, such as the yam, the taro,

the banana, &c., there are a number of food-plants now growing wild, but

rarely cultivated, and only used when the others fail. These plants,

which include the wild yams, the mountain bananas, Tacca pinnatifida,

Pandanus odoratissimus, and several others, are regarded as older than

the Polynesians in the Pacific, and as having probably formed the food

of a pre-Polynesian race that practised only a rude sort of cultivation.

(3) The weeds of Polynesia also fall into two groups. In the first place

there are the aboriginal weeds, of which those found in this region by

Captain Cook’s botanists in the latter part of the 18th century are

taken as examples. These include species of Urena and Sida, besides

Waltheria americana, Oxalis corniculata, Bidens pilosa, and many other

weeds. In the second place, there are the numerous weeds that are known

to have been introduced by the white man since the voyages of the

English and French navigators of Captain Cook’s time.

(4) There is reason to believe that many weeds now cosmopolitan in the

tropics had obtained their present distribution in America and in the

Old World before the Polynesians entered the Pacific. It is thus that we

can explain how there existed in these islands at the time of their

discovery by Cook, Bougainville, and other navigators of that period, a

number of weeds that have their homes in America.

(5) It is not considered that the distribution of aboriginal weeds can

materially aid the ethnologist in his study of the early history of man,

since birds are regarded as the chief distributors of their seeds and

fruits. Whilst man has prepared the conditions for the growth of weeds,

the bird has usually brought the seeds.

(6) Amongst interesting plants concerned with man in the Pacific are

Aleurites moluccana and Inocarpus edulis, which are regarded as in the

main distributed through man’s agency. Gyrocarpus Jacquini is viewed as

a tree originally widely dispersed by the currents in the Pacific, but

now becoming extinct.

CHAPTER XXIX

BEACH AND RIVER DRIFT

In the south of England.—On the coast of Scandinavia.—In the

Mediterranean.—Southern Chile.—Very little effective dispersal by

currents in temperate latitudes.—Cakile maritima.—In tropical

regions.—River drift.—River and beach drift of Fiji.—Musa Ensete.—The

coco-nut.—River and beach drift of Hawaii.—Comparison of the beach

drift of the Old and New Worlds.—Summary.

THE BEACH DRIFT OF TEMPERATE LATITUDES

DISPERSAL by currents seems to be mainly restricted to warm latitudes.

Whilst in the tropics seed-drift is abundant on the beaches, in the

cooler regions of the globe it is usually very scanty and often masked

by other vegetable _débris_.

Let us take, for instance, a beach in the south of England. We can find

by careful searching amongst the stranded drift the seeds and

seed-vessels of various littoral plants of the buoyant group, such as

Arenaria (Honckeneya) peploides, Cakile maritima, Crithmum maritimum,

Convolvulus soldanella, Euphorbia paralias, &c., and such sundries as

bits of stems of Salsola kali bearing fruits; but their amount is

scanty; and they are often difficult to find on account of the great

amount of rubbish with which they are associated, such as empty stones

of cherries, plums, and peaches; empty seeds of grapes; hazel-nuts,

beech-nuts, chestnuts, acorns, all either empty or with decaying seed;

the spiral pods of Medicago; besides quantities of leaves, sticks, and

bark. Although the occasional shell of a Spirula, or the horny skeleton

of a Velella, or a genuine pumice pebble (see Note 76), may tell us of

long wanderings in mid-ocean, we find little that is not English or

derived from neighbouring coasts on a beach in the south of England. I

have examined numerous beaches on the coasts of Devon and Cornwall, and

have never come upon any indubitable tropical seed-drift.

On one occasion I examined many of the beaches between Ilfracombe and

Padstow with the object of finding tropical seeds, but to no purpose.

Portions of bark, generally 2 to 4 inches across and much water-worn,

together with a quantity of steamer-slag or cinders, often largely

composed the stranded drift. No doubt this bark is stripped off by the

waves from floating trees, which are generally stranded in a bare

condition after a long ocean voyage. This is the case with the timber

brought in the Oregon drift to Hawaii; and Sernander (p. 117) remarks

that bark seldom occurs on the trees washed ashore with the Atlantic

drift on the coasts of Scandinavia. Modern marine deposits ought to

contain much bark _débris_.

On the beaches in the vicinity of estuaries we find a certain amount of

river drift, and amongst it fruits or seeds of Sparganium ramosum, Iris

pseudacorus, Alnus glutinosa, Rumex, and many other river-side plants,

such as I have mentioned in my paper on the Thames drift (_Journ. Linn.

Soc. Bot._, xxix). Most of them are capable of reproducing the plant,

but not on the sandy beach where the waves have stranded them; and we

thus see here one of the limits of the efficacy of currents as

seed-dispersers.

From the labours of Lindman and Norman, the results of which are summed

up by Sernander (p. 116) we can learn what are the components of the

“Atlantic Drift” on the Scandinavian coast; and a strange assortment we

here find, in which it is difficult to detect much indication of

effective seed dispersal. Besides the seeds of Cæsalpinia Bonducella,

Entada scandens, and Mucuna urens, familiar to us as occurring in the

drift of tropical beaches, there is a quantity of vegetable drift

hailing sometimes from North America, sometimes from the Canary Islands,

and sometimes from the West Indies, mingled with much local drift in

which the larch and steamer-slag or cinders predominate. The seed-drift

derived from the proper beach-plants of the coast plays a subordinate

part, though it is stated by Norman and others that seeds and

seed-vessels, as the case may be, of Arenaria peploides, Cakile

maritima, Convolvulus soldanella, and Lathyrus maritimus, with those of

other plants, are also to be found.

The Mediterranean beach drift, as illustrated by the results of my

examination of numerous beaches in Sicily as well as in the islands of

Stromboli and Lipari, and of the beach at Cumæ, is of a scanty nature.

If we eliminate the various evidences of cultivation which seem to occur

over much of the temperate regions of the globe, very little remains of

an interesting character. As in the south of England and in other

regions, the empty stones of the cherry, plum, and peach, the empty nuts

of the oak, hazel, &c., together with the spiral pods of Medicago figure

largely in the drift; and here and there we come upon the seeds of

littoral plants, such as Convolvulus soldanella and Euphorbia paralias.

I have found Medicago fruits in all these localities on the beaches.

They often contain seeds, which, it may be added, have no buoyancy, the

seeded pods themselves floating from two to five days. The pods of

several kinds of Medicago form the great feature of Sicilian drift and

are often indications in other places of the vicinity of cultivated

districts. A small hairy species thrives on Letojanni beach near

Taormina, and I observed its seeds together with those of Euphorbia

paralias germinating in the drift stranded on the same beach. Arcangeli,

in his _Flora Italiana_, enumerates as many as thirty-three species of

Medicago. Many of the species grow in maritime districts, and their

fruits must often get into the beach drift independently of cultivation.

I noticed the pods amongst the drift brought down by the Alcantara, a

river near Taormina, a fact which goes to explain their presence in

beach drift.... On the beach of Trogilus Bay, near Syracuse, I gathered

several fruits of a Vitex, apparently V. agnus castus. After being kept

afloat for six weeks in sea-water some were placed in soil, when they

soon germinated and reproduced the plant.

The beach drift of temperate Chile is described in Chapter XXXII. There,

as in other beaches of cool latitudes, it is not easy to find seeds

amongst the rubbish; but amongst the scanty seed-drift may be recognised

much of what we are familiar with in the Old World, such as the seeds of

Convolvulus soldanella, bits of the fruiting stems of Salsola kali, as

well as the rubbish indicating the white man’s presence, such as empty

stones of cherry, plum, and peach, Medicago pods, &c. In addition, we

find the seed-vessels of plants like Franseria and Nolana that are

peculiar to American beaches; and now and then, the seeds of Sophora

tetraptera, a tree of the immediately adjacent hill-slopes, come under

our notice.

Before quitting this subject of the beach seed-drift of temperate

latitudes, it may be observed that when at San Francisco I visited the

beach running south from the Golden Gate. With the exception of the

fruits of Cakile maritima, a plant growing on the beach, few other seeds

or fruits were observed in the drift.

The inference that there is very little effective dispersal by currents

in temperate regions is of some importance, and Sernander arrived at a

similar conclusion when discussing the origin of the Scandinavian flora.

The few plants with buoyant seeds and fruits, such as Arenaria

peploides, Cakile maritima, Crithmum maritimum, Convolvulus soldanella,

Euphorbia paralias, and Lathyrus maritimus, are no doubt thus dispersed,

and Norman is quite right in attaching some value to the distribution by

currents of certain plants within the region of the Arctic flora; but

after all it amounts to little, and geographical and climatic conditions

have often had a predominant influence in determining the distribution

in the temperate latitudes of littoral plants possessing buoyant seeds

or fruits.

Nowhere is this shown more plainly than with the littoral plants with

buoyant seeds or seed-vessels that are found on our English beaches.

Some have evidently acquired their present distribution before ice and

snow reigned supreme in the extreme north. Though it may be possible, it

seems highly improbable, that either Arenaria peploides or Lathyrus

maritimus, both of which occur on beaches in high northern latitudes in

the Atlantic and Pacific Oceans (as in Arctic Norway, Spitzbergen, and

Behring’s Straits), could possess in our own day any means of

communication between their areas of distribution on the borders of

these two ocean-basins.

So again with Cakile maritima, the occurrence of this or of two closely

allied species on both sides of North America cannot be attributed to

any present working of the currents for two reasons. In the first place,

as is remarked in Note 18, the results of two independent experiments

made by me show that the fruits will not float more than a week or ten

days in the sea, a capacity that will not admit of their transportation

by the currents over tracts of ocean more than one or two hundred miles

across. In the second place, this species is not an Arctic plant like

Arenaria peploides and Lathyrus maritimus; and the possibility of

inter-communication between the Atlantic and Pacific Oceans having any

effective value from the standpoint of dispersal, shadowy as it is with

the two Arctic species, is still more so in the case of Cakile maritima.

Norman’s observations on the coast of Norway, as quoted by Sernander

(page 123), indirectly indicate how hopeless it would be for this plant

to attempt to traverse the Arctic region. Just as I have noticed on the

north coast of Devonshire, the fruits occur plentifully in the beach

drift and germinate freely in the upcast wrack as far north as Senjen in

latitude 69°. Further north the plant has been recorded from only eight

localities, and since it is there sterile and but a summer annual, the

seed-vessels, it is argued, must have been brought by the currents from

the south.

The reference to Cakile maritima as a summer annual on the north coast

of Norway is of interest; but I may point out that it displays a similar

behaviour in England on the north coast of Devonshire. Here, during the

latter half of July, 1903, I found the fruits common in the stranded

drift, and often in a germinating condition, whilst numerous seedlings

one to two inches high with the fruit-shell still attached were growing

out of the sand. From this arises the curious reflection that an annual

which germinates in the end of July could scarcely be expected to mature

its fruit before the winter. It would seem that this beach plant hampers

its own dispersal by its misdirected efforts; and the idea suggests

itself that we have here the explanation of its sterility in the north

of Norway. Had it been a perennial like Arenaria peploides and Lathyrus

maritimus it might have had a similar distribution within the Arctic

Circle.

Quite other considerations seem to be suggested by the perennials

Crithmum maritimum and Euphorbia paralias. In these cases, although the

seeds or fruits, as the case may be, will float for months in sea-water

without apparently sustaining any injury, the species are confined to

the warmer parts of the European region.

From Convolvulus soldanella we obtain another story. Its occurrence in

the temperate regions of both the northern and southern hemispheres,

great as the floating powers of the seeds may be, is concerned with

something more than with questions relating to modes of dispersal. The

circumstance that in its distribution in the temperate regions it is

practically coterminous with Ipomœa pes capræ in the tropics is very

significant (see Note 49).

Each one of the English beach plants with buoyant seeds and fruits has

its own story of the past to tell. Time has indeed gathered on our

beaches current-dispersed plants, which, if they could speak, would tell

us strange stories of many latitudes, stories of change within the

Arctic Circle, and stories of great events within the temperate regions,

and, as in the case of Convolvulus soldanella, stories of a past within

the tropical zone. It cannot be said that investigators lack clues

leading to lines of inquiry into the age that immediately precedes our

own.

Yet valuable as our British plants would be for this purpose, they do

not afford any indication that currents have played an important part in

plant distribution in temperate and arctic latitudes. Ekstam strikes the

true note for these regions when discounting the agency of currents in

the instance of the Spitzbergen flora, he regards the wind as the

greatest factor in seed-dispersal and after that the bird. The several

interesting points raised by this botanist are discussed in Chapter

XXXIII.

THE BEACH-DRIFT OF TROPICAL LATITUDES.

Tropical beaches, as a rule, present a much greater abundance and

variety of stranded seeds and fruits than we find on beaches in

temperate latitudes. Observers in different parts of the tropics have

alluded to the enormous amount of vegetable drift floating in the sea

off the coasts, particularly in the vicinity of estuaries. Though much

of it is brought down by rivers, a good proportion is also derived from

the luxuriant vegetation that lines the beaches. Gaudichaud speaks of

the immeasurable quantity of drift (trees, branches, leaves, flowers,

fruits, and seeds) floating amongst the islands of the Molucca Sea; and

Hemsley, who quotes this author, gives other facts illustrating the same

point. Moseley tells us that seventy miles off the coast of New Guinea,

H.M.S. _Challenger_ found the sea in places blocked with drift (_Bot.

Chall. Exped._ iv. 279, 284). When the author of this book was in the

Solomon Group, long lines of vegetable drift were frequently observed

floating among the islands. The Rewa River in Fiji carries down a great

amount of drift to the sea; and as described in Chapter XXXII, the

Guayaquil River in Ecuador bears seaward an enormous quantity of these

materials.

When we come upon this floating drift out at sea off an estuary, we

find, as Mr. Moseley pointed out, that the leaves have gone to the

bottom, whilst the floating islets, composed of the matted vegetation

lifted up from the shallows of a river channel, which form such a

feature in the Guayaquil River, have been dispersed or sent to the

bottom. However, a very large proportion of the seed-drift brought down

by a river from the interior has no effective value for the purposes of

dispersal. Many of the fruits and seeds brought down from inland owe

their presence in river-drift entirely to the buoyancy acquired by the

decay of the seeds. It is in its lower course when it traverses the

mangrove belt that a river picks up most of the material that is of

service in distributing the species; and this is mingled out at sea with

the numerous buoyant seeds and fruits of littoral plants that are swept

off the beaches by the currents.

A description is given in Chapter XXXII of the enormous amount of

vegetable drift brought down by the Guayaquil River to the coast of

Ecuador. Besides the huge tree-trunks and the floating Pistias, we

observe large islets formed mainly of Pontederias and Polygonum,

together with a host of seeds and seed-vessels, both large and small,

including those of Anona paludosa, Entada scandens, Erythrina, Hibiscus

tiliaceus, Ipomœa, Mucuna, Vigna, &c., accompanied by the empty seeds of

Phytelephas macrocarpa and of many other strange plants from the slopes

of the Chimborazo mountains. In addition, we notice the seedlings of

Avicennia and of Rhizophora mangle together with the seeded joints of

Salicornia peruviana and the germinating fruits of Laguncularia.

When in Fiji I made an especial study of the drift of the Rewa Estuary

within tidal influence, the results of which are incorporated in various

parts of this work. In the rainy season, when the drift is most

abundant, the following would be its most characteristic components:

Seedlings of Bruguiera and Rhizophora.

Fruits of Barringtonia racemosa and B. speciosa, the first-named most

abundant and often germinating.

Seeds of Carapa obovata, most of them far advanced in germination.

Fruits of Lumnitzera coccinea.

Fruits of Cerbera odollam, abundant.

Fruits of Inocarpus edulis, with the seed generally rotten.

Fruits of Heritiera littoralis, Parinarium laurinum, and Pandanus.

Empty seeds of Aleurites moluccana.

Fruits of Scirpodendron costatum, abundant.

Fruits of Clerodendron inerme and Smythea pacifica, both of them in

some cases germinating.

Pyrenes of Morinda citrifolia.

Small fruits of Vitex trifolia and Premna taitensis, both sometimes

abundant.

Seeds of Entada scandens, Mucuna, and Vigna lutea.

Pods of Dalbergia monosperma and Derris uliginosa, the last sometimes

in a germinating condition.

Seeds of Hibiscus tiliaceus and of different species of Ipomœa, such as

I. peltata and I. pes capræ.

Amongst other seeds and fruits brought down by the Fijian rivers and

stranded with a large amount of miscellaneous vegetable _débris_ on the

beaches in the vicinity of the estuaries are the seeds of Dioclea,

Strongylodon lucidum, and Afzelia bijuga; the empty seeds of Musa Ensete

(as identified with a query at Kew); the empty stones of the Sea tree,

apparently a species of Spondias; the seeds of Colubrina asiatica; the

fruits of an inedible indigenous Orange (Citrus vulgaris?) referred to

in Chapter XIII; the cocci of Excæcaria Agallocha and Macaranga; and

Coco-nuts.

The occurrence in Fijian beach-drift of the seeds of Musa Ensete, or of

a wild banana much like it, is very remarkable. This species is found in

the mountains of Abyssinia and on the slopes of Kilima-njaro in

Equatorial Africa; but according to the monograph by Schumann on the

Musaceæ (Engler’s _Pflanzenreich_, 1900) the species is confined to

Africa, whilst all the other species of the subgenus are mostly

restricted to the same continent with the exception of one or two in

Further India. The empty seeds are frequent on the beach at Duniua at

the mouth of the Ndreke-ni-wai in Savu-savu Bay, Vanua Levu, and are

doubtless brought down by that river. Strangely enough the natives could

give me no information about the parent plant which I never discovered.

The seeds did not come under my notice in any other locality in Fiji.

They answer to the description and to the figure given by Schumann for

Musa Ensete; and their presence in the drift is one of the mysteries of

the Pacific floras.

To enumerate the seeds and fruits found stranded on beaches in Fiji

would be to give a list of all the littoral plants with buoyant seeds or

fruits that are included in the list given in Note 2. I may here allude

to the fact that the Coco-nut, whether brought down by a river or

transported by a current, is able to germinate and establish itself when

washed up on the Fijian beaches. I have found these fruits germinating

amongst the drift stranded on the beaches near the mouths of rivers,

some just beginning to germinate and others already striking into the

sand and showing the first leaves. White residents living for years in

one locality were quite convinced that this frequently happens. One of

them pointed out to me some newly formed land at a river’s mouth, not

over two years old, on which were growing young plants three or four

feet high of Barringtonia speciosa, Calophyllum Inophyllum, and several

other plants including young Coco-nut palms, all growing from fruits

washed up by the waves and therefore self-sown.

Like the littoral flora the beach-drift proper to the Hawaiian Islands

is very scanty. This is due to the scarcity of rivers, to the absence of

the mangrove-formation from which much of the drift is derived in other

tropical regions, and to the paucity of shore-plants with buoyant seeds

or fruits. As is observed in Note 30, where the composition of the beach

drift is described, the presence of a large amount of timber and of

other materials brought by the currents from the north-west coast of

America masks much of the local drift.

Remarks on the beach-drift of the Panama Isthmus, and of the Ecuadorian,

Peruvian, and Chilian coasts of South America will be found in Chapter

XXXII. I have examined beach drift in other tropical regions, as in the

Solomon group, on Keeling Atoll, and on the south coast of West Java;

whilst there are at my disposal the data supplied by Schimper and Penzig

for the Malayan region including Krakatoa, and by Hemsley for tropical

regions generally. It will, I think, be best, if instead of describing

in detail the composition of the drift for each locality, I refer

briefly to the features that distinguish the tropical beach-drift of the

Old World from that of the New World.

The beach-drift reflects the characters of the coast flora; and since

tropical littoral floras belong to two great regions, the Asiatic

including Polynesia and the African East Coast, and the American

including the African West Coast, the seeds and fruits stranded on the

beaches may be similarly referred to the same two regions.

All over tropical Asia, as well as in the tropical islands of the Indian

and Pacific Oceans, the drift stranded on the beach presents the same

general character, and as a rule possesses seeds and fruits of the same

species that range over the whole or the greater part of this region.

Almost everywhere we find seeds or fruits of the same plants of the

beach formation, such as Barringtonia speciosa, Cæsalpinia Bonducella,

Calophyllum Inophyllum, Canavalia obtusifolia, Cerbera Odollam, Cordia

subcordata, Entada scandens, Guettarda speciosa, Hernandia peltata,

Hibiscus tiliaceus, Ipomœa pes capræ, Mucuna, Scævola Kœnigii, Sophora

tomentosa, Terminalia Katappa, and Tournefortia argentea. In those

localities where mangrove-swamps occur we find generally diffused in the

stranded drift of this region the seedlings of Bruguiera and Rhizophora,

the seeds of Carapa moluccensis, the fruits of Heritiera littoralis and

Lumnitzera coccinea, and the pods of Derris uliginosa. Amongst sundries

found over much of this region may be mentioned, the drupes of Pandanus,

the seeds of Erythrina, Vigna lutea, and Hibiscus tiliaceus, and the

“nuts” of Aleurites moluccana. With the exception of the last-named all

the fruits and seeds here enumerated are effectively dispersed by

currents over great areas. The sound nuts of Aleurites have no buoyancy;

and the nuts only acquire their floating power through the decay of the

kernel (see p. 419).

The beach drift of the American region, a region which comprises both

the Pacific and Atlantic coasts of tropical America as well as the

African West Coast, has some features in common with the Asiatic

beach-drift and other features peculiar to itself. The plants, however,

that are represented in the drift of both regions are comparatively few,

and none of the large fruits of the Asiatic region are here to be

noticed. We observe, however, that the drift of the two regions possess

in common the seeds of Cæsalpinia Bonducella, Canavalia obtusifolia,

Entada scandens, Erythrina, Mucuna, Sophora tomentosa, and Vigna lutea,

all belonging to the Leguminosæ; and to these we must add the seeds of

Hibiscus tiliaceus and of Ipomœa pes capræ, and the seedlings of

Rhizophora and Avicennia. (Avicennia occurs in tropical Asia, but not in

Polynesia.) The distinctive characters of the beach-drift of both coasts

of America and of the west coast of Africa would be shown in the

presence of seeds of Anona paludosa, the fruits of Laguncularia

racemosa, Conocarpus erectus, Spondias lutea, and other plants. But the

beach-drift of the American region is much more scanty. Of the shore

plants generally dispersed in this region there could not be more than a

couple of dozen that are indebted for their wide dispersal to the

currents, and these alone figure in the effective beach drift. In the

Asiatic region these plants would number at least seventy or eighty.

_Summary._

(1) Effective dispersal by currents is mainly restricted to warm

latitudes, as is indicated by the scanty character of the seed-drift

stranded on the beaches of the south of England, Scandinavia, the

Mediterranean, and Southern Chile.

(2) The present distribution in temperate latitudes of littoral plants

possessing buoyant seeds or seed-vessels is to be attributed more to the

influence of geographical and climatic conditions than to the agency of

currents. With some of them, such as those that occur on both sides of

North America, it is evident that their distribution antedates the

present climatic conditions within the Arctic Circle.

(3) Time has gathered on an English beach current-dispersed plants that

could tell us strange stories of many latitudes.

(4) The seed-drift that is often found in such abundance in tropical

seas is partly brought down by rivers and partly swept off the coast.

Very little of the seed-drift brought down by the rivers from the

interior is of any service for plant-dispersal, nearly all the floating

seed-drift found at sea which has any effective value being derived from

the plants of the beach and of the mangrove belt.

(5) The tropical beach drift of the Old and New Worlds reflects the

characters of the littoral floras of those regions, more especially with

regard to the plants provided with buoyant seeds or seed-vessels. The

plants represented in the beach drift common to both these regions

belong mostly to the Leguminosæ. The large fruits so characteristic of

Old World beach-drift are not found in the New World. The number of

shore plants with buoyant seeds or seed-vessels that are widely

dispersed in the American region are only one-quarter or one-third of

those in the Old World region; and this difference is reflected in the

scanty character of tropical American beach-drift.

CHAPTER XXX

THE VIVIPAROUS MANGROVES OF FIJI

RHIZOPHORA AND BRUGUIERA

_Rhizophora._—Represented by Rhizophora mucronata, Rhizophora

mangle, and the Selala, a seedless intermediate form.—Their

mode of association and characters.—The relation of the

Selala.—Polyembryony.—The history of the plant between the

fertilisation of the ovule and the detachment of the seedling.—Absence

of a rest period.—Mode of detachment of the seedling. Capacity

for dispersal by the currents.—_Bruguiera._—The mode of

dispersal.—Peculiar method of fertilisation.—Length of period between

fertilisation and the detachment of the seedling.—Mode of detachment

of the seedling.—Summary.

BETWEEN 1897 and 1899 I made numerous observations on the Fijian species

of Rhizophora and Bruguiera (mostly around the coasts of Vanua Levu and

in the Rewa delta); and these were supplemented in the early part of

1904 by observations on the first-named genus in Ecuador. I did not make

any collections in Fiji until Prof. Schimper asked me to obtain

specimens; and a fair-sized collection containing specimens dried, and

preserved in spirit, was sent to him. His illness and death shortly

followed, and I lost the advantage of his great experience in these

matters. In a letter written to me in 1898 he expressed the hope that I

would publish my notes on the mangroves of Fiji. Years have since passed

by, and as I read again his words of encouragement I take up once more

the interrupted task.

RHIZOPHORA

Of the three species of this genus, two of them, Rhizophora mucronata

and R. conjugata, are Asiatic and are unknown in America; whilst the

third, R. mangle, was until recently regarded as peculiar to the

American and West African regions.

When Mr. Hemsley wrote the Report on the Botany of the Challenger

Expedition he remarked (iii, 149) that the American Rhizophora (R.

mangle) appeared to be restricted to that region, and he questioned its

existence in the Pacific Islands as indicated by Jouan for New

Caledonia. The same view was taken by Prof. Schimper in his work on the

Indo-Malayan strand-flora published in 1891. There was, in fact, much to

support this view, since Dr. Seemann, one of the most accomplished

botanists who have explored the Pacific, describes only the Asiatic

Rhizophora (R. mucronata) in Fiji, and nothing is said of any other

species collected by the United States Exploring Expedition under Wilkes

in Fiji and Samoa.

However, in a paper on the flora of Tonga, read before the Linnean

Society in 1893, Mr. Hemsley includes the American mangrove, Rhizophora

mangle, amongst the collections made there by Mr. Lister; and he refers

to its occurrence also in Stewart Island (I suppose in the Solomon

Group), but he suggests that it was accidentally introduced with ballast

in both these localities. In 1897 I found a species of Rhizophora, to

all appearances identical with the American species, in great abundance

in the Rewa delta in Fiji. Subsequently the same mangrove came under my

notice as the prevailing species in Vanua Levu in the same group; and on

sending photographs of a branchlet in flower and fruit and of the

germinating fruit to Prof. Schimper he expressed the opinion that they

belonged to the typical Rhizophora mangle.

There are four typical mangroves in Fiji, namely (1) Bruguiera rheedii,

the “Dongo” proper of the natives; (2) Rhizophora mangle, usually known

as “Tiri-wai,” that is to say, the Tiri of the river, or rather of the

estuary; (3) Rhizophora mucronata, the “Tiri-tambua” of the Fijian,

signifying the Whale’s Tooth Tiri in allusion to the form of its fruit;

and (4) a seedless form intermediate between the two species of

Rhizophora, which the Fijians designate “Selala,” a name signifying “the

tree with empty flowers.”

Bruguiera rheedii and Rhizophora mucronata were alone recorded by Dr.

Seemann and his predecessors; but he significantly refers to the natives

speaking of four mangroves. Mr. Horne, who spent twelve months in the

group some years later, also overlooked the American Rhizophora; but it

is apparent that both these botanists were naturally more interested in

the vegetation of the inland regions than of the coast swamps, and we

have before observed that they failed to record Scirpodendron costatum,

a giant-sedge very common and conspicuous in the swamps. It is not easy

to understand Dr. Seemann’s remark that “mangroves are restricted to but

few parts of the larger islands.” Horne, who was in the islands eighteen

years afterwards, makes frequent allusion to them. The natives whom I

questioned closely on this subject scouted the idea that any of the four

mangroves above named were recent arrivals. The coasts, as they said,

had always been extensively fringed by mangroves; and the reader has

only to refer to my remarks in the second chapter of my volume on the

geology of Vanua Levu to convince himself that mangrove swamps of

considerable extent existed in the time of Commodore Wilkes (1840).

_The Relative Abundance and Mode of Association of the three Fijian

forms of Rhizophora._

Stated in their order of frequency, we have first Rhizophora mangle, the

American species, then Rhizophora mucronata, the Asiatic species, and

lastly the Selala. The first is equally at home at the sea-border and on

the banks of brackish estuaries. The second is, as a rule, more

exclusively at home on the sea-coasts; and the same may be said for the

Selala. Usually all three kinds occur in the lower part of an estuary;

but as we ascend the river and the water freshens, the Asiatic

Rhizophora and the Selala disappear, and the American plant is alone

found in the higher reaches, where the density of the water ranges

according to the state of the tide between 1·000 and 1·010. I examined

the distribution of these three forms of Rhizophora in numerous

estuaries of Vanua Levu, as well as in the Rewa estuary in Viti Levu;

and it was ascertained that in all cases they followed the rule above

indicated. When the estuary receives but few streams and the water is

mostly salt, the three Rhizophoras may extend miles inland; but when it

contains a large body of fresh-water, Rhizophora mangle may be the only

form observed from the mouth of the river to the head of the estuary,

and it may monopolise the adjacent coasts. On the other hand, Rhizophora

mucronata may occupy almost exclusively a long extent of coast; or the

Selala may prevail in certain localities, as on parts of the Mathuata

coast of Vanua Levu.

The manner of association of these three Rhizophoras is of interest in

connection with the origin of the seedless Selala. They very rarely

occur mingled together, but grow gregariously in contiguous colonies;

and not uncommonly all three may occur on the same line of coast within

a distance of a few hundred yards. The colonies pass into each other

without a break, and there is no fixed rule of association. Whilst on

the south side of Vanua Levu the Selala is generally associated with the

American Rhizophora, on the north side it is usually in touch with the

Asiatic species. In other localities all three occur in contiguous

colonies. The Selala colony may be exposed on the line of a river-bank

or along the sea-coast, or it may lie in the heart of an extensive

mangrove tract. The most extensive mangrove region in Fiji, that of the

Rewa delta, is in great part occupied by Rhizophora mangle; but all

three forms grow together in the eastern part of the delta; and here,

strangely enough, as at Daku, the Selala may grow sporadically, and all

three may grow mixed together with their branches intercrossing.

_The Characters of the Selala or Seedless Rhizophora compared with those

of the American Mangrove (R. mangle) and the Asiatic Mangrove (R.

mucronata)._

The three kinds of Rhizophora, when seen at the same time along a tract

of coast, may be readily distinguished by the different shades of green

of their foliage, that of Selala being dark green, that of Rhizophora

mucronata light green, and that of Rhizophora mangle intermediate in

shade. The Selala is usually the tallest of the three, and attains a

height of from 20 to 30 feet or even 40 feet and over, the aerial roots

dropped from the higher branches giving it a characteristic aspect.

Rhizophora mangle is generally the shortest, and at the coast is from 10

to 12 feet high; but where the mangrove vegetation is most luxuriant, as

in the great swamps in the interior of the Rewa delta, it forms tall

trees as much as 40 feet in height, displaying the aerial roots hanging

from the higher branches. Rhizophora mucronata is, as a rule,

intermediate in height, and is distinguished by its stout, reddish trunk

and reddish aërial roots.

The trunks of Selala are often in an inclined position and supported

entirely by the trestle-like aërial roots, the lower end raised some 5

or 6 feet above the ground with the rest of the trunk inclined upwards.

They then look like gigantic walking-stick insects. The same habit may

be sometimes observed with the larger trees of Rhizophora mucronata, and

in fact all three may present at times the same habit of growth. The

taller trees of Rhizophora mangle may resemble the Selala in habit, and

the smaller trees of the Selala may approach the habit of Rhizophora

mangle.

The distinctive characters of the Selala are given in the table

opposite. It will be there seen that this form is intermediate between

the other two species as regards the form and size of the petioles and

peduncles; the size of the bracts and bracteoles; the colour, form, and

size of the flowers; and in the length of the style. Its leaves are

smaller than in the case of the other two species, but pointed and

semi-aristate like those of Rhizophora mucronata. There are, however,

two varieties of the Selala, both with larger foliage than that

belonging to the prevailing type of the tree, and from 10 to 15 feet in

height. In one the flowers are more numerous, each flowering stem

branching four or five times and bearing at least twenty-four flowers,

the first branch being trichotomous and the rest dichotomous. In the

other, which is the prevailing form on the Mathuata coast, there is a

nearer approach to Rhizophora mucronata in the rounding of the peduncles

and in the length of the style. Then, again, there are divergent

varieties of Rhizophora mangle which in the larger bracts and bracteoles

and in the greater size, form, and paler hue of the flowers come nearer

to the Selala. Taking all the characters together, the Selala, though

intermediate between the Asiatic and the American species, comes in the

most critical diagnostic points, as in the inflorescence, in the

individual flowers, and in the form of the apex of the leaf, nearest to

Rhizophora mucronata, the Asiatic species.

The seedless character of the Selala is well known to most Fijians of

the coast districts, the native name signifying empty (lala) flowers

(se). Now and then they aver that it produces fruit, but the numerous

offers of rewards in money never resulted in their bringing me the

fruits. During my residence of two years in the group I examined the

Selala trees in a great number of localities and never succeeded in

finding them in fruit.

With all three kinds the anthers burst in the bud before it begins to

open, and we may ask why the process of self-fertilisation, which is

effectual with the other two kinds, produces no result with the Selala.

In all three cases the flower-buds and expanded flowers hang downwards,

and the expanded flowers retain their parts for the first twenty-four

hours, the pollen being caught in quantity on the hairy edges of the

petals. During the next day the withering stamens fall out, and on the

following day the petals fall too. With the Selala, the style soon

begins to blacken and wither, and in a few days the flower becomes

detached and drops off. With Rhizophora mucronata and Rhizophora mangle,

the style preserves its healthy condition, and shortly evidences of

fertilisation appear in the altered shape of the ovary. It is apparent,

therefore, that in the case of the Selala fertilisation has not

occurred, although the mechanical processes connected with it have been

carried out. The cause of this is not far to seek.

+-----------------+--------------------------------------------------------+

| | FIJI |

| CHARACTERS +------------------+------------------+------------------+

+-----------------+------------------+------------------+------------------+

| in feet | 12-20. | 20-40. | 9-12. |

| | | | |

| | | | |

| | | | |

| | | | |

| | | | |

| | | | |

|Peduncle (lowest}|Rounded. |Flattened above. |{Flattening more |

| flower-stalk) }| | |{marked than with |

| | | |{Selala. |

| | | | |

| | | | |

| bracteoles |(4 mm.). |(2 mm.). |absent. |

| | | | |

| |4-1/2 - 5 lines | |(8 mm.). |

| |(11-12 mm.). | | |

| | | | |

| |(4 mm.). | |(1·5 mm.). |

| | | | |

| | | | |

| roots |Reddish. | — | — |

+-----------------+------------------+------------------+------------------+

+-----------------+-------------------------------------+

| | ECUADOR. |

| CHARACTERS. +------------------+------------------+

| |RHIZOPHORA MANGLE |RHIZOPHORA MANGLE |

| | (Mangle chico). | (Mangle grande). |

+-----------------+------------------+------------------+

|Height of tree in| 10-15. | 50-80 and more. |

| feet | | |

| | | |

|Colour of foliage|Pale green. |Dark green. |

| | | |

|Base of leaf |Tapering or |Tapering. |

| |sub-rounded. | |

| | | |

|Apex of leaf |Very obtuse, with |Very obtuse, with |

| |no twisted point. |no twisted point. |

| | | |

|Leaf-stalk |Flattened above |Flat above with a |

| (petiole) |and below, with no|median groove, |

| |median groove, |1 inch (25 mm.) |

| |1/2 inch (12 mm.) |long, two-thirds |

| |long; not half as |the length of the |

| |long as the |peduncle. |

| |peduncle. | |

| | | |

|Inflorescence |As described under|Branching at least|

| |R. mangle of Fiji.|three times, |

| | |sometimes four or |

| | |five times, |

| | |trichotomous or |

| | |dichotomous, |

| | |twelve to |

| | |forty-eight |

| | |flowers. |

| | | |

|Peduncle (lowest}| | |

| flower-stalk) }|}Sub-angular. |Rounded. |

| | | |

|Pedicels |More slender than |More slender than |

| |the peduncle, and |the peduncle, and |

| |rounded. |angular. |

| | | |

|Bracts and |Scarcely |Well developed, |

| bracteoles |developed, 1/2 |1 line (2·5 mm.). |

| |line (1 mm.). | |

| | | |

|Calyx |As with R. mangle |As with R. |

| |of Fiji. |mucronata and |

| | |Selala of Fiji, |

| | |but lobes 4 lines |

| | |(10 mm.). |

| | | |

|Length of style |Less than a line |1-1/2 lines |

| |(2·5 mm.). |(4 mm.). |

| | | |

|Fruit |As in R. mangle of|Conical, not |

| |Fiji. |symmetrical, and |

| |(Hypocotyl 9 or |somewhat curved; |

| |10 inches.) |large persistent |

| | |bracteoles at base|

| | |as in R. |

| | |mucronata. |

| | |(Hypocotyl 12 to |

| | |15 inches.) |

| | | |

|Colour of trunk, | | |

| rootstock and | | |

| roots | — | — |

+-----------------+------------------+------------------+

Although the ovaries of the Selala contain four ovules, which in size

and appearance do not differ from those of Rhizophora mangle and R.

mucronata, its pollen when compared with that of the other two forms

presents a remarkable difference. The pollen of these three mangroves

was examined in five localities far apart from each other, and in all

the same results were obtained. The pollen-grains of the Selala are much

smaller than those of the other two, and differ much from them in form.

They are irregularly oval in outline, and have a shrunken look beside

the spherical symmetrical grains of the two species with which they are

compared. They are from one-fourth to one-third the size of those of

Rhizophora mucronata, and from one-third to one-half the size of those

of Rhizophora mangle.

There is much to support the view that the Selala is a cross between the

other two species, its intermediate characters and its seedless

condition being especially indicative of such a derivation; but there

are several difficulties in accepting this explanation.

(1) The circumstance of the anthers bursting in the flower-bud would

considerably lessen the chances of cross-fertilisation; but this

objection is not insurmountable, since numerous insects, such as flies,

ants, and small coleoptera, visit the newly opened flowers, and they

might sometimes produce a result. When I made this suggestion to Prof.

Schimper he replied that insect-pollination was quite possible after the

expansion of the flowers.

(2) If, as seems highly probable, the pollen of Selala is impotent

and the ovules fertilisable, then its seedless condition implies not

only an incapacity for self-fertilisation, but also for

cross-fertilisation; and if Selala with its impotent pollen does not

admit of cross-fertilisation, this would still less be expected of

Rhizophora mucronata and R. mangle where the pollen is potent and

where fertilisation takes place in the bud. I endeavoured to

fertilise the Selala flowers with the pollen of the two other

species; but there were no results, the flowers falling off in a few

days. It may here be remarked that on one Selala tree I found a

solitary flower with an enlarged ovary, as if through fertilisation.

(3) It is not easy to explain the gregarious growth of the Selala if it

is a seedless hybrid. The colonies could not be renovated by mere

intercrossing, especially in places where, as on the north coast of

Vanua Levu, the dense belt of mangrove is for many miles composed in

mass of Selala trees, with a few trees of the Asiatic and American

Rhizophoras growing on the outskirts.

It is obvious that in order to clear the way for considering this

problem the means of renovating the Selala colonies should be inquired

into. In the first place, whilst seedlings occur in numbers under the

trees of the other two Rhizophoras they are never to be found under the

Selala trees. The mode of reproduction of the Selala is evidently

vegetative, and the question arises as to what mode of vegetative

reproduction occurs. The Selala trunks, as already observed, are often

inclined, the trunks being supported on trestle-like aërial roots. These

trunks send out branches which in their turn drop aërial roots; and when

the decay of the parent trunk takes place, the branches are able to live

independently. The primary branches in due time send out secondary

branches which also let fall aërial roots; and thus the process is

repeated indefinitely, the result being a maze of semi-prone trunks,

branches, and aërial roots. The first stage of the process ends with the

death of the parent trunk, and the primary branch, supported by its own

aërial roots, is often all that the observer can distinguish in the

centre of a colony. This is evidently the mode by which the Selala

colonies are renovated in their interior. One sometimes observes in the

midst of one of these colonies extensive bare mud-flats 100 to 500 yards

across from which apparently the trees have died off _en masse_. The

natives assert that when part of a Selala tract is cleared the trees

never grow again.

But _pari passu_ with this process of vegetative reproduction of the

Selala, by which the mass of the colony is preserved and renovated,

there is evidently some other process of reproduction in operation

amongst the trees of Rhizophora mangle and R. mucronata at the edge of

the colony, as a result of which Selala seedlings are produced. Whilst

no seedlings are to be observed striking into the mud under the Selala

trees, numbers occur, as before observed, under the trees of the other

two species. Those under the trees of R. mangle possess in nearly all

the cases the distinctive leaf-characters of that mangrove, and would be

recognised at once as belonging to that species. On the other hand,

those beneath the trees of R. mucronata are of two kinds, some of them

being readily recognised by their foliage as of the Selala type others,

again, being typical seedlings of R. mucronata. Only those seedlings, or

“keimlings” as we might term them, were noted that had dropped plumb

from the branches above.

Such were the results of my investigations on Vanua Levu. My field of

inquiry was then shifted to the Rewa delta, where, with the assistance

of the Daku natives, who, like most Fijians, display a keen interest in

matters relating to their plants, I spent a few days in investigating

the origin of the Selala trees that grow sporadically in that locality.

On pulling up some of the young trees we found that the original

radicular or hypocotyledonary portion of the keimling could be still

distinguished. My zealous native friends also pointed out to me that

though the leaves in form and colour were those of the Selala, the

rootstock was reddish like that of R. mucronata, and not white as with

R. mangle. The natives averred that the Selala trees are produced in the

first place from fruits of R. mucronata. When young, they said, they are

Tiri-tambuas (R. mucronata), but when old, Selalas. Yet although R.

mucronata may be now regarded as the source of the Selala trees, and my

Vanua Levu observations pointed unmistakably in this direction, it could

not be definitely settled whether this was the result of a cross with

the male element of R. mangle or whether the Tiri-tambua (R. mucronata),

in producing two types of seedlings, one fertile with the parent

characters and the other seedless of the Selala type, brought about the

same end. On the whole I am inclined to the view that the Asiatic

Rhizophora presents us in the dimorphism of its seedlings the true

explanation.

This inference is supported by the behaviour of Rhizophora mangle on the

coast of Ecuador, a subject which is discussed in Chapter XXXII, and I

have given the results of my observations on the Ecuadorian Rhizophoras

side by side with those on the Fijian trees in the table before given.

There are two very distinct forms of the American Rhizophora (R. mangle)

in the swamps of Ecuador. There is the low coast tree, the “Mangle

chico” of the Ecuadorians, ten to fifteen feet in average height, which

grows on the sea-front of the swamps and has all the general appearance

and the more conspicuous characters of the American Rhizophora in Fiji.

There is also a tall tree, 60, 80, or even 100 feet high, that forms the

great mass of the mangrove swamps. In its inflorescence, in the dark

green colour of its foliage, and in other characters, it comes near the

Fijian Selala; but it differs in fruiting abundantly. This is locally

termed the “Mangle grande,” and its true relation to the Fijian Selala

appears to be as follows. Whilst both as regards the flowers approach

the Asiatic Rhizophora (R. mucronata), the Fijian Selala resembles the

Asiatic tree also in its foliage, whilst the “Mangle grande” or the

Ecuadorian Selala more resembles the typical American tree (R. mangle)

in its leaves and also in its seedlings. Here in the Ecuadorian swamps

there can be no question of crossing, since both, according to Baron von

Eggers, belong to one species. Therefore I am inclined to the opinion

that whilst the Asiatic Rhizophora displays dimorphism in Fiji, the

American Rhizophora displays dimorphism in Ecuador. The reversion on the

part of the “Mangle grande” of Ecuador to some of the characters of the

Asiatic plant is remarkable, and points to the greater antiquity of the

Asiatic R. mucronata as compared with the American R. mangle.

This accords with the opinion expressed by Schimper in his work on the

Indo-Malayan strand flora that the American Rhizophora is either a

degenerated descendant of the Asiatic R. mucronata or a sister form

derived from a common ancestor. America, as we have seen, possesses only

one of the three species of Rhizophora, and this is the only

representative that it owns of the four Asiatic genera (Rhizophora,

Kandelia, Ceriops, Bruguiera) that constitute the tribe Rhizophoreæ. The

rule prevailing with current-dispersed plants that America is a

distributor and not a recipient evidently does not apply to the

Rhizophoreæ; and to explain their distribution we must go back to some

epoch very remote from the present. That Fiji derived its

representatives of Rhizophora mangle from America by the agency of the

currents I do not for a moment admit. The restriction of the species and

indeed also of the genus to the Western Pacific is very significant. It

is far more likely that, as I have pointed out in the case of Lindenia

(see page 396), the American Rhizophora was once widely distributed over

the tropics of the Old and New Worlds, and that it is now on the “down

grade” towards extinction. Its survival in the Western Pacific could

thus be explained without our being obliged to suppose that the

seedlings or keimlings have been carried uninjured across the Pacific

Ocean, an ocean voyage for which, as shown in a later page, they are not

well fitted.

_The Occasional Occurrence of more than one Seed in the Fruits of

Rhizophora mucronata and Rhizophora mangle (Polyembryony)._

The bilocular ovary contains four ovules, one of which only as a rule

becomes a seed. But it is incorrect to say that the fruits are always

one-seeded, since two or even three seeds are occasionally produced, and

they may all germinate. In November, 1897, I noted eight hundred fruits

of Rhizophora mangle germinating on the trees in one of the creeks of

the Rewa delta. Out of this number eight fruits had two germinating

seeds and one had three, the protruding radicles being in all stages of

growth. Just two years afterwards I counted eight hundred more fruits in

the same locality, and then observed seven with two germinating seeds

and none with three, the radicles protruding in all cases. On another

occasion at Wailevu in Savu-Savu Bay I counted four hundred, and none

had more than a single radicle protruding. The results appear to vary

with the locality, but in the Rewa creek the proportion of fruits in

which more than one seed germinated was fairly constant at dates two

years apart, namely, about one per cent. Occasionally, however, in

particular localities a greater proportion may be noticed. Thus near

Daku in the Rewa delta I found that the proportion was between two and

three per cent. for the same species (R. mangle), those with three

germinating seeds being about half per cent.

The case of more than one seed germinating in the fruits of Rhizophora

mucronata never came under my observation; but in one locality, where I

examined a considerable number of fruits near the stage of germination,

between ten and fifteen per cent. showed two seeds approaching maturity.

Warming thoroughly investigated the polyembryony of Rhizophora more than

twenty years ago, seemingly from materials brought to him from the West

Indies (Engler’s _Botanische Jahrbücher_, band iv., 1883). With the

usual German thoroughness he deals with the work of earlier observers,

and goes back to Piso in the middle of the 17th century. Of the four

ovules, he remarks, three usually abort, and only in rare cases are two

seeds developed. He quotes Baron von Eggers to the effect that only in

three per thousand cases was more than one seedling observed protruding

from a germinating fruit. These remarks evidently all apply to the

American species. I do not find any reference in my notes to

polyembryony in Ecuador, and evidently its occurrence is not so frequent

there as in Fiji.

It is frequently apparent in the cases where more than one seed

germinates in a fruit that on account of the difference in the length of

the protruding seedlings germination does not always begin at the same

time. Thus in Fiji the difference in the length varied between one and

three inches, an amount representing at least from ten to twenty days’

growth, as will be subsequently pointed out. Warming in one of his

figures gives a fruit where an interval of some months seems to be

indicated, since one of the seedlings has fallen out and the other is

protruding less than an inch. By cutting across a fruit containing two

seeds one may sometimes observe one seed quiescent and the other

beginning to germinate. The significance of this occasional interval

between the germination of seeds in the same fruit will be referred to

in a later page.

_The Seasons of Flowering and Fruiting of the Species of Rhizophora in

Fiji._

The Selala flowers all the year. With the two American and Asiatic

species there are considerable variations between different localities.

Generally speaking, they flower and fruit all the year through; but the

flowers are usually less abundant in the warm season from December to

February, and the germinating fruits which are to be observed on the

trees every month of the year are more numerous in that season.

_The History of the Reproductive Process in Rhizophora from the

Fertilisation of the Ovule to the Falling of the Plantlet or Seedling

from the Tree._

I devoted great attention to this subject in the instance of Rhizophora

mangle, being desirous of determining two points, in the first place as

to whether there was any period of rest between the maturation and

germination of the seed, and in the second place as to the period that

elapsed between the commencement of germination and the fall of the

seedling.

The principal change in the ovary for the first three or four weeks

after fertilisation is shown in its increased breadth. The increase in

height is but slight during this period; and in fact after thirty days

the ovary only added 2 millimetres to its original height of 3

millimetres. After this the growth of the fruit proceeds until the tip

of the radicle pierces its summit, the fruit being then about eleven

lines (2·8 cm.) long. _From the date of fertilisation to the time the

radicle pierces the top of the fruit a period of about fifteen weeks

elapses._ (The fruit, it should be here remarked, continues to grow in

length and breadth after the radicle has protruded, attaining a length

of thirteen or fourteen lines [3·5 cm.] when the seedling or “keimling”

is ready to fall.)

By referring to the table below it will be observed that there is no

period of rest in the growth of the fruit up to the date of the

protrusion of the radicle. It will now be shown that there is normally

no pause between the epoch of the maturation of the seed and the

beginning of germination, or, in other words, that from the time of the

fertilisation of the ovule to the onset of germination there is no

cessation in the process of growth of the embryo. That period of dormant

vitality which almost all seeds pass through forms no normal feature in

the life-history of this species of Rhizophora.

RHIZOPHORA MANGLE AND R. MUCRONATA.

+-------------------------------------------+

| RHIZOPHORA MANGLE. |

+-------------------------------------------+

| _Growth of fruit in height._ |

+---------------------+---------------------+

| Lines or tenths of | Number of days |

|an inch (millimetres | since |

| in brackets). | fertilisation. |

+---------------------+---------------------+

| | |

| 2 (5) | 30 |

| 3 (7·5) | 42 |

| 4 (10) | 50 |

| 5 (12·5) | 61 |

| 6 (15) | 67 |

| 7 (17·5) | 74 |

| 8 (20) | 83 |

| 9 (22·5) | 92 |

| 10 (25) | 100 |

| 11 (28) | 105 |

| | { Protrusion|

| | 107{ of the |

| | { hypocotyl |

| |

| _Growth of the protruding hypocotyl._ |

| |

| 10 (25) | 127 |

| 20 (50·5) | 141 |

| 30 (76) | 151 |

| 40 (101·5) | 160 |

| 50 (127) | 167 |

| 60 (152) | 175 |

| 70 (177·5) | 185 |

| 80 (203) | 202 |

| 90 (228) | 222 |

| | {Fall of |

| | 229{the |

| | {seedling |

+---------------------+---------------------+

_Explanation of the Table._

We have here shown the period between fertilisation and the fall of the

seedling from the tree.

This period divides itself into two parts, the first being concerned

with the continuous growth of the fruit and of the inclosed embryo until

the tip of the hypocotyl appears through the apex of the fruit, the

second being indicated by the growth of the protruding hypocotyl until

the fall of the seedling.

The height of the fruit is measured from the base of the calyx-lobes,

and the length of the hypocotyl at first from the apex of the fruit and

afterwards from the edge of the protruding neck of the cotyledonary

body. The height of the ovary at the time of fertilisation is about 3

millimetres; and from that time onward it is to be regarded as a fruit.

[_To face page 452._

FIGURES ILLUSTRATING THE DEVELOPMENT OF

THE SEED AND THE GERMINATING PROCESS

OF RHIZOPHORA AND BRUGUIERA

(Natural size. Drawn for convenience of description in the erect

position.)

1. Rhizophora mucronata Fruit 3-1/3 lines (8-9 mm.) high, six to

seven weeks after fertilisation. The

micropyle is but slightly dilated, and is

occupied by a small plug of endosperm.

2. Rhizophora mucronata Seed of fruit represented in Fig. 1.

3. Rhizophora mucronata Fruit 5 lines (12 mm.) high, eight to nine

weeks after fertilisation. Germination is

about to begin. A large plug of endosperm now

protrudes through the dilated micropyle, but

still covers the lengthening hypocotyl.

{Seed of fruit represented in Fig. 3. In

4.} Rhizophora mucronata {Fig. 4 the plug of endosperm is shown on the

5.} {upper end of the seed; whilst in Fig. 5 it

{has been removed, exposing the tip of the

{hypocotyl.

6. Rhizophora mucronata Fruit 7-1/2 lines (18 mm.) high, eleven to

twelve weeks after fertilisation.

7. Rhizophora mucronata Fruit, seventeen or eighteen weeks after

fertilisation.

8. Rhizophora mucronata Full-grown fruit with upper portion of

seedling just before detachment from the

tree. The long tapering plumule is here

inclosed in the cotyledonary body. The *

indicates the point of detachment of the

seedling.

9. Rhizophora mucronata The cotyledonary body of Fig. 8.

9A.} {Illustrating different stages in the

9B.}Rhizophora mucronata {development of the plumule and of the neck of

9C.} {the cotyledonary body resulting finally in

9D.} {the expulsion of the plumular end of the

{seedling from the fruit cavity as in Fig. 8.

{(See page 458.)

10. Rhizophora mucronata Fruit with two seeds.

FIGURES ILLUSTRATING THE DEVELOPMENT OF

THE SEED AND THE GERMINATING PROCESS

OF RHIZOPHORA AND BRUGUIERA—(_continued_)

(Natural size. Drawn for convenience of description in the erect

position.)

11. Rhizophora mangle Fruit, six weeks after fertilisation.

12. Rhizophora mangle Seed with plug of endosperm, as shown in Fig. 11.

13. Rhizophora mangle Fruit, eight weeks after fertilisation. The tip of

the hypocotyl is now piercing the plug.

14. Rhizophora mangle Embryo (enlarged) shown in Fig. 13.

15. Rhizophora mangle Fruit, ten weeks after fertilisation. The growing

hypocotyl has now pierced the plug.

16. Rhizophora mangle Embryo shown in Fig. 15.

17. Rhizophora mangle Fruit, nearly sixteen weeks after fertilisation.

18. Rhizophora mangle Full-grown fruit, just before the detachment of the

seedling from the tree. The long tapering plumule

is inclosed in the tube of the cotyledonary body.

The point of detachment of the seedling is

indicated by *.

19. Rhizophora mangle The cotyledonary body of Fig. 18.

20. Rhizophora mangle Fruit with two seedlings in different stages of

growth (given in the first plate).

21. Bruguiera Rheedii Fruit, about four weeks after fertilisation. (The

shaded portion is the calyx-tube or cup, in the

midst of which rises the style.)

22. Bruguiera Rheedii Germinating seed.

23. Bruguiera Rheedii Germinating fruit, about eight weeks after

fertilisation.

24. Bruguiera Rheedii Germinating fruit, about ten weeks after

fertilisation. Here the growing hypocotyl,

carrying the style with it, has pushed upwards the

lining membrane of the floor of the calyx-tube,

which has ruptured and forms a cap on its extremity.

25. Bruguiera Rheedii Germinating fruit, thirteen or fourteen weeks after

fertilisation.

26. Bruguiera Rheedii Fruit with full-grown seedling just before its

detachment from the tree.

[_To face page_ 453.

RHIZOPHORA MUCRONATA.

_Growth of the first seven inches of the hypocotyl after it protrudes

from the fruit._

10 lines (25 mm.) after 26 days

20 lines (50·5 mm.) after 41 days

30 lines (76 mm.) after 51 days

40 lines (101·5 mm.) after 61 days

50 lines (127 mm.) after 70 days

60 lines (152 mm.) after 78 days

70 lines (177·5 mm.) after 86 days

In my description of the germinating process of Rhizophora mangle from

this particular standpoint I adopt the general views of Prof. Schimper,

the observations being my own, the phraseology employed being his. It

would be out of place here to deal with the biological significance of a

process to which observers like Warming, Goebel, Karsten, Schimper and

Haberlandt have applied their greater talents as well as their greater

experience. I investigated the subject carefully from my own standpoint

of inquiry, and whilst the reader will find in my rough sketches of the

various stages of the process a little aid in following the argument, he

is referred for detailed treatment of the subject to the memoirs of the

above-named botanists as well as to those of yet more recent

investigators.

After fertilisation, according to Prof. Schimper (_Ind. Mal.

Strandflora_), the embryo-sac is filled with endosperm, which

subsequently protrudes and forms a plug completely closing the micropyle

(see my figures). As my observations showed, the seed during the first

eight weeks after fertilisation increases continuously in size, and the

plug of endosperm, at first inconspicuous, becomes of considerable size,

the seed attaining a length of seven millimetres. The embryo meanwhile

grows rapidly, and at the end of this period of eight weeks the

radicular tip or the point of the hypocotyl begins to protrude from the

micopyle, still covered by the plug of endosperm, the fruit being

between four and five lines (10-12 mm.) in length (figures 11-14). In

another week, when the fruit has grown another line in length, the tip

of the radicle is on the eve of piercing the plug, and this may be

termed _the commencement of germination, nine weeks after the act of

fertilisation_. The next stage, after an interval of one and a half

weeks, is illustrated in figure 15; and _after a period of about fifteen

weeks from the date of fertilisation the tip of the radicle pierces the

top of the fruit_. As shown in the figures, the fruit grows in length

throughout the process.

The question as to whether the matured seed passes through a stage of

quiescence before it germinates finds its answer in the statement that

only nine weeks elapse between fertilisation and germination. It may,

however, be urged that the maturation of the seed could be accomplished

in a few weeks, and that after this a period of dormant vitality might

follow. This objection can be at once disposed of and the whole matter

placed beyond reasonable doubt by making, as I did, a large number of

vertical sections of the fruit in all its stages. It will then be

perceived that there is a fairly constant relation in all stages of

growth between the seed and the fruit, whether maturating or

germinating. Since the growth of the fruit is continuous (see Table) up

to the time of the protrusion of the tip of the hypocotyl through its

coats, it follows that there can be no appreciable pause between the

completion of maturation and the commencement of germination of the

seed. In other words, both fruit and seed preserve the same relation

during the process, and the absence of any period of rest is to be

inferred from the uninterrupted growth of the fruit.

We will take, to illustrate this point, a fruit between four and five

lines long in the stage that immediately precedes germination (see

figure 11). The fruit proceeds with its growth, and the seed, we will

suppose, remains quiescent for a month. At the end of that time (see

Table) the fruit would be eight lines long, and the seed, of course,

would be unchanged. This condition of things never presented itself to

me. Fruits eight lines long were always far advanced in germination (see

figure 15). If the seed passes through an interval of rest before

germination, it must be of a very short duration and practically _nil_.

This absence of any period of rest between the final maturation of the

seed and its fertilisation had already been assumed by Prof. Schimper.

Writing to me on July 14, 1898, when my observations were in progress,

he says:—“I am ready to assume, according to my own experience, that

there is continuous development until the falling off of the embryo.

More accurate observations on the subject would be interesting, and

would not present any great difficulties.” At the end of the same month

he wrote the preface to his great work on Plant-Geography; and he

expresses himself decidedly on this point. Speaking of Rhizophora

mucronata (English edition, p. 396), he says that “the fruit ... soon

after the completion of its growth is pierced at its summit by the green

hypocotyl, as the embryo does not undergo any period of rest, but

continues to develop without interruption.”

Though the rest-period is normally non-existent with the seeds of

Rhizophora, it has already been observed that it is indicated in rare

cases and under exceptional conditions. Thus I have already remarked

that in Fiji about one per cent. of the germinating fruits of the

American species exhibit more than one seed. These seeds usually begin

to germinate about the same time, but in a few cases, say, one in ten, a

marked difference in the length of the protruding hypocotyls points to

the fact that one of the seeds began to germinate some weeks after the

other. We at times also meet with fruits which when cut across display

two seeds, of which only one is beginning to germinate. Such cases

indicative of a pause between the maturation of the seed and the

beginning of germination would be very rare. With Rhizophora mangle,

probably one in a thousand fruits would be a generous estimate.

In passing it may be remarked that the same stages occur with Rhizophora

mucronata in the development of the seed and in the subsequent

germinating process. When the fruit is three lines long the micropyle is

but slightly dilated (see figures 1 and 2). When it is four lines long

the endosperm begins to escape from the gaping micropyle and forms a

projecting plug. The growth of the embryo now becomes rapid, the

endosperm escapes in greater quantity, and by the time the fruit is five

lines long the tip of the radicle is on a level with the micropyle,

although still covered by the plug (see figures 4, 5). After this,

germination begins; and when the fruit is six lines in length the

radicle is in the act of penetrating the plug. Ultimately the tip of the

radicle pierces the top of the fruit when this last is nine or ten lines

long. As shown in the figures there is continuous growth of the fruit

during the maturation and germination of the seed, until, in fact, the

plantlet drops into the water. With reference to the stage when

germination begins, it should be remarked that the formation of the

large plug of endosperm outside the micropyle does not necessarily

indicate the beginning of germination. Germination is in progress only

when the hypocotyl or radicle begins to lengthen and is on the point of

piercing the plug of endosperm that fills up the gaping micropyle. This

is well shown in this species in the case of fruits with two seeds. Both

seeds may have large plugs of endosperm, and yet only one may show

indications of germination in the lengthening hypocotyl.

We must now return to the subject of the growth of the hanging seedling

of Rhizophora mangle. We have already remarked that, as shown in the

Table, about fifteen weeks (107 days) is the average time elapsing

between the fertilisation of the ovule and the protrusion of the tip of

the radicle through the top of the fruit. A further period of seventeen

and a half weeks (122 days) is occupied by the growth of the seedling on

the tree, at the end of which period it drops into the water or mud

according to the state of the tide. This gives a total period of nearly

thirty-three weeks (229 days) as the duration of the time between

fertilisation and the fall of the seedling. This may be divided, as has

been already implied, in the following manner:—

(1) Period between fertilisation and germination. 9 weeks.

(2) Period between the commencement of germination 6-1/2

and the protrusion of the tip of the radicle weeks.

through the top of the fruit.

(3) Period occupied by the growth of the hypocotyl 17-1/2

outside the fruit, and terminating in the fall weeks.

of the seedling from the tree.

——

Total 33 weeks.

This represents the average of numerous observations, the deviations

being from two to three weeks on either side. In the latter part of its

growth, the lower end of the hypocotyl becomes thickened or club-like,

and during the last week or ten days the increase in length is arrested

altogether.

My observations on the growth of the seedling on the tree of Rhizophora

mucronata were comparatively few; but, as shown in the Table on page 453

they give nearly the same rate of growth. Taking the average length

attained by the hypocotyl on the tree at sixteen inches, and employing

as well the data supplied by Rhizophora mangle, a period of 26-1/2 weeks

would elapse from the time the hypocotyl pierces the top of the fruit

until the plantlet falls from the tree. If we then add, as in the case

of the other species, 15-1/2 weeks for the preceding period between

fertilisation and the protrusion of the hypocotyl, we get a total of 42

weeks for the whole period from fertilisation to the fall of the

seedling. In the extreme cases where a length of almost two feet is

attained on the tree, the period would somewhat exceed twelve months;

and in those rare instances in other regions, when, according to

Schimper, the seedling is a metre in length, probably eighteen months

would be required. The period for Rhizophora mucronata is thus

considerably longer than for R. mangle, which is sufficiently indicated

by the difference in the average length of their hypocotyls on the tree

in Fiji, that for R. mucronata being sixteen inches, and that for R.

mangle nine or ten inches.

The only other observations that have come under my notice relating to

this subject are those made by Jacquin on Rhizophora mangle in the West

Indies in the middle of the eighteenth century. The results are

literally quoted by Warming; but I have referred to the original account

in the work of Jacquin, entitled _Selectarum Stirpium Americanarum

Historia_, Vindobonæ, 1763. According to this observer the seedling

falls from the tree in the twelfth month from the fecundation of the

flower. This happened in my observations on the same species in Fiji in

the eighth or ninth month. Jacquin states that the tip of the radicle

protrudes from the fruit in the third month, whilst my results give it

as taking place in the fourth month. The difference in the length of the

total period, it may be remarked, would be to a great extent determined

by the varying length acquired by the seedling before it drops from the

tree. In ordinary conditions it averages about ten or eleven inches, and

the hypocotyl itself attains a length of nine or ten inches on the tree,

both in Fiji and Ecuador; but in sheltered localities it may attain a

length half as long again. I have already pointed out in the case of the

fruits of Rhizophora mucronata that a year and more would be sometimes

required, and the same remark would apply to unusually long fruits of R.

mangle. Local conditions would often produce varying results, both in

the rate of growth of the hanging seedling and in the duration of the

period of its attachment to the tree; but it is probable that nine or

ten months would represent for the genus the average length of the

period between fertilisation of the ovule and the detachment of the

seedling from the parent tree.

_The mode of separation of the seedlings of Rhizophora mangle and

Rhizophora mucronata_

This is a process of expulsion almost akin to parturition, and is

brought about by the outward growth of the neck of the cotyledonary

body. There is much that is of great interest in this subject; and I may

add that Haberlandt, in a memoir published in the _Annales du Jardin

Botanique de Buitenzorg_ for 1894, gives the results of an elaborate

study of the viviparous process in this and other genera of mangroves.

The same analogy seems also to have presented itself to him, but only in

connection with the means employed in some of the genera, as with

Bruguiera, for conveying nourishment to the growing embryo. He remarks

that he was involuntarily reminded by these structures of the

chorion-tufts and lobes in the placenta of mammals, and that such

structures in the mammal are functionally nothing more than true

_haustoria_ as found in the viviparous mangroves.

When studying the germination of the American and Asiatic Rhizophoras in

Fiji, I observed that the neck of the cotyledonary body did not begin to

form, nor the inclosed plumular bud to show signs of differentiation,

until the hypocotyl had protruded about 4-1/2 inches with R. mangle, and

between 6 and 7 inches with R. mucronata. The neck of the cotyledonary

body then proceeds to grow in length, pushing before it the plumular end

of the embryo-seedling, which it surrounds as a sheath. This operation

continues until the hypocotyl has acquired a length of about seven

inches with R. mangle, and about nine inches with R. mucronata, when the

neck begins to protrude outside the fruit. The cotyledonary neck

proceeds with its growth, and by the time the seedling is ready to fall

from the tree it protrudes about an inch from the fruit-shell, having

carried the growing plumular bud with it. The plumular end of the

seedling has been now more or less expelled from the fruit-cavity, and

the connection between the suspended seedling and the fruit now alone

depends on a slight bond between the base of the plumule and the inner

margin of the cotyledonary neck, as indicated by a cross in the figures

given in the plate. The union is soon broken and the seedling falls.

Whether there is anything more than an analogy between the expulsion of

a Rhizophora seedling and the birth of a mammal seems most unlikely; but

the process is at all events a very remarkable one.

_The means of dispersal of the genus Rhizophora_

My experiments and observations were for the most part made on the

Asiatic and American species in Fiji; but I enjoyed the opportunity of

confirming some important points on the coast of Ecuador. We can only

look to the currents for the explanation of the capacity of the genus to

cross tracts of ocean; but, given this capacity, there is much that is

difficult to understand in the distribution of the genus and of a

species like Rhizophora mangle; and it is probable that we shall have to

look behind the means of dispersal to a distant age in the distribution

of shore-plants of the mangrove type.

When Schimper published his work on the Indo-Malayan strand flora in

1891, but little was known of the duration of the floating capacity of

Rhizophora seedlings (p. 166). In giving the results of my

investigations I am merely describing the agencies of dispersal at

present in operation. Such agencies have their limitations, and we may,

perhaps, be thus able to explain why Rhizophora is restricted in the

Pacific islands to the archipelagoes of the Western Pacific; but many

serious objections would at once present themselves if we regarded the

occurrence of the genus in America, as well as in Asia and Africa, as a

matter depending on capacities and means of dispersal.

The fruits of Rhizophora, as they display themselves before the

protrusion of the germinating seed, have no buoyancy, and the

germinating fruits until the hypocotyl has protruded for some inches (6

inches in the case of R. mangle) also sink in sea-water. With a further

increase in the length of the hypocotyl, the germinating fruit acquires

buoyancy; and when the seedling, usually 10 or 11 inches in length,

becomes detached from the fruit on the tree and falls into the sea, it

floats readily in 95 per cent. of the cases. Such seedlings occur very

commonly in the floating drift of the estuaries and out at sea both in

Fiji and in Ecuador.

Out of five seedlings of the Asiatic species, Rhizophora mucronata, that

had fallen naturally from the tree, three were afloat and healthy after

eighty-seven days’ immersion in sea-water. Out of twenty seedlings of

the American mangrove, Rhizophora mangle, sixteen floated after ninety

days and four were afloat and healthy after one hundred and twenty days,

the greater number sinking during the fourth month. These results

indicate considerable powers of buoyancy, and go to show that extensive

tracts of ocean could be traversed by the floating seedling.

Observations of a Naturalist in the Pacific Between 1896 and 1899, Volume 2 Plant-Dispersal · 第 42 / 47 章

One can imperfectly distinguish two sets of food-plants in this region;