Now, what are these changes? How has the_Observations of a Naturalist in the Pacific Between 1896 and 1899, Volume 2 Plant-Dispersal

determining part? These are questions which I will endeavour in some way

to answer as one picks one’s path slowly through the various epochs in

the plant-history of these islands. We already are fairly well

acquainted with the beginnings of a flora either on a coral atoll or on

an ordinary tropical beach. What we have yet to learn is the subsequent

history of the flora. When Dr. Treub undertook, in 1886, his now

celebrated examination of the new flora of Krakatoa after the great

eruption, he commenced a series of observations which will no doubt be

prolonged into future centuries. Botanists a hundred and two hundred

years hence will complete a long chain of observations which will be

unique as a record of plant-colonisation; and science is deeply indebted

to Prof. Penzig for making, in 1897, the second examination of the new

flora. Though deprived of the valuable record that future generations

will possess for Krakatoa, we yet have at our disposal in the completed

process displayed by many a Pacific island a means of working backward

and in a sense completing the history.

In order to attack this problem I have mainly confined myself to the

Fijian, Tahitian, and Hawaiian floras, taking the three archipelagoes

just named as the centres of the regions in which they occur. These

three groups lie near the three angles of the triangular area of the

Pacific over which the various archipelagoes are scattered. They are

thus geographically well placed for an inquiry into the subject of

plant-dispersal over this ocean, and each of their floras has been

investigated by botanists of various nationalities—American, Austrian,

British, French, German, and Italian. The Fijian area may be regarded as

including the adjacent Samoan and Tongan groups, though the individual

group or the whole area will always be in this work particularised. In

the same way Tahiti will be viewed as usually representative of the

larger islands of the surrounding groups of the Cook and Austral Islands

and of the Marquesas; and under the designation of the Tahitian area or

Tahitian region there will be generally included the Paumotu

archipelago.

COMPARISON OF THE AREAS AND ALTITUDES OF HAWAII, FIJI, AND TAHITI.

Since differences in physical conditions have played an important part

in plant distribution in these groups—such, for instance, as in

determining the development of a mountain flora or in favouring the

relative abundance of particular types of plants—it is at first

essential to obtain a general idea, in the case of the larger islands of

each group, of their size and elevation, and of the more conspicuous

differences in their climates.

Hawaii, the largest island of the Hawaiian archipelago, has an area of

4,210 square miles. All the other islands of the group are considerably

smaller—Maui, the second in size, having a surface of 760 square miles;

Oahu coming next; and after it Kauai, with an area of 590 square miles.

The area of Viti Levu, the largest island of the Fijis, is 4,112 square

miles, being thus closely similar to that of the island of Hawaii; Vanua

Levu, the second in size, is 2,433 square miles in extent; whilst the

other important islands of the group are much smaller, Taviuni, the

third in size, having an area of 218, and Kandavu an area of 125 square

miles. Tahiti, the largest and loftiest island of Eastern Polynesia, has

a surface of about 400 square miles; whilst most of the other elevated

islands of the groups around are considerably smaller.

In respect of elevation above the sea, there is a great contrast between

the islands of these three regions. Taking the Hawaiian Group first, we

notice that the three principal mountains of the large island of Hawaii

rise in the cases of Mauna Kea and Mauna Loa to between 13,000 and

14,000 feet, and in that of Hualalai to rather over 8,000 feet. Situated

between these three mountains there is an extensive tableland or

plateau, known as the Cattle Plains, which is elevated between 4,000 and

6,000 feet, and has an area of not less than 200 square miles. At least

a third of the whole area of the island exceeds 4,000 feet in altitude.

In the eastern portion of Maui the huge mass of Haleakala rises to

rather over 10,000 feet; whilst Mount Eeka, in West Maui, rises in bulk

to some 6,000 feet. The island of Kauai, which is elevated between 5,000

and 6,000 feet, possesses in its interior an elevated tableland 40

square miles in extent and 4,000 feet in altitude. Oahu attains in Mount

Kaala a maximum elevation of 4,000 feet, but 3,000 feet is the limit of

the other peaks, and much of the island is low in elevation.

On the other hand, in the two largest islands of Fiji, namely, Viti Levu

and Vanua Levu, we find in the first-named only two or three of the

highest mountain peaks rising to between 4,000 and 5,000 feet; whilst

the highest peak of Vanua Levu reaches only to about 3,500 feet. Amongst

the lesser islands, Taviuni just reaches the level of 4,000 feet, and

Kandavu, the next in height, about 2,750 feet. The area of the

land-surface in this group that is above a level of 4,000 feet is very

scanty, and for the botanist a negligible quantity, so that for purposes

of comparison the Fijian Islands, as far as elevation is concerned,

correspond to the lower levels of the Hawaiian Islands, that is, to the

areas below 4,000 feet. The same may be said of the Samoan Islands with

the exception of a limited area in the centre of Savaii, where a peak

rises to 5,400 feet above the sea.

Coming to the Tahitian region, we find that Tahiti, the most elevated

island, attains an extreme height of about 7,300 feet; but from its

surface-configuration it is evident that not one-tenth of the area

exceeds 5,000 feet; yet since its total extent is about 400 square miles

there must be an elevated region of some 30 square miles in amount

comparable in some degree with the uplands of Hawaii. The Marquesas,

next in order in size and height, attain a maximum elevation of about

4,000 feet; whilst, amongst the Cook and Austral Groups, Rarotonga

reaches a height, according to Mr. Cheeseman, of 2,250 feet. Excepting

the limited elevated area of the uplands of Tahiti, there is nothing in

Eastern Polynesia corresponding to the higher levels of the Hawaiian

Islands over 4,000 feet. We formed the same conclusion for Fiji, and I

may add that it applies to the whole area of Fiji, Samoa, and Tonga,

since the solitary peak of Savaii in the second-named group, which

reaches 5,400 feet, alone represents a high-level area. The uplands of

Hawaii—that is to say, the elevated region between 4,000 or 5,000 feet

and 14,000 feet (strictly speaking 13,800 feet)—are therefore almost

unrepresented amongst the Oceanic groups of the South Pacific; and it is

only in the peak of Savaii and in the limited high levels of Tahiti that

we would expect to find their conditions reproduced. The great effect

that this contrast implies in determining differences between the floras

of the Hawaiian, Fijian, and Tahitian regions will become apparent as we

proceed in this discussion.

COMPARISON OF THE CLIMATES OF HAWAII, FIJI, AND TAHITI.

Before comparing the climatic conditions in the three groups, it may

first be remarked that since they lie, roughly speaking, at not very

dissimilar distances north and south of the equator a great contrast is

not to be expected in so far as they agree in elevation. The mean

latitudes do not differ greatly, that of Hawaii being 20° to 21° N., and

those of Fiji and Tahiti both about 18° S. The climate of both groups is

tempered by the north-east trade in the one region and by the south-east

trade in the other. Still there is a difference in the temperature and

dryness of the air which noticeably distinguishes Hawaii from Fiji, and

to a less extent from Tahiti. The mean temperature of the Hawaiian

Islands would be 74° or 75°; whilst that of Tahiti is placed at 76° to

77°, and that of Fiji at 79°. But it is to be observed that to a person

residing in Fiji after a residence in Hawaii the climate is perceptibly

warmer, more humid, and more enervating. No doubt this is in part

connected with the greater dryness of the air in Hawaii, where the

average relative humidity at Honolulu is placed at 72 per cent., and it

must be much less on the Kona coast on the dry side of the largest

island. It is, however, probable that the Hawaiian climate was less dry

before the destruction of the forests, and that the contrast with the

Fijian climate was then less pronounced.

The great distinguishing feature, however, of the Hawaiian Islands is to

be found in their mountain climate. This is not represented in Fiji, but

slightly in Samoa, and to a small extent in Tahiti; and I will now refer

more particularly to this important subject.

In the uplands of the large island of Hawaii, on the tops of the lofty

mountains 10,000 to 14,000 feet above the sea, we have a mean

temperature only found far north. Snow lies often on these barren

summits in winter, more particularly on Mauna Kea, which thus derives

its native name of the White Mountain. The details of my meteorological

observations on Mauna Loa will be found in Note 61; and only some of the

general results will be referred to here.

The mean temperature for the period of twenty-three days passed by me on

the summit of Mauna Loa (13,600 feet) between August 9th and 31st, 1897,

was 38·5° F. The mean temperature for a period of twenty days from

December 24th, 1840, to January 12th, 1841, during which Commodore

Wilkes and his party were making pendulum observations on the summit of

the same mountain, was approximately 33·5° (see Note 61). From these

results, which are tabulated below, it will be seen that the mean annual

temperature would be probably about 36°, which is scarcely comparable

with any continental climate, since only a difference of a few degrees

is indicated between the mean temperatures of August and of a similar

period in mid-winter. I may add that although it was in the summer month

of August, water froze inside my tent during twenty out of the

twenty-three nights passed on the top. We may, therefore, infer that the

temperature falls below the freezing point at night practically

throughout the year. It will be seen from the table that the mean annual

temperature for the summit of Mauna Loa, as here computed from the

observations of Commodore Wilkes and myself, comes very near to that

which might be estimated by employing Hann’s tables of variation in

temperature with altitude on tropical mountains (see Schimper’s

_Plant-Geography_, iv. 691).

WINTER AND SUMMER TEMPERATURES ON THE SUMMIT OF MAUNA LOA

(13,600 FEET), IN DEGREES FAHRENHEIT.

+---------+---------------+--------------+-------+--------+--------+------------+

+---------+---------------+--------------+-------+--------+--------+------------+

|Wilkes |Dec. 24, 1840- |17°-50°=33° | 13° | 55°? | 33·5° | } |

| |Jan. 12, 1841 | | | | | } |

| | | | | | | } 36° |

|Guppy |Aug. 9-31, 1897|23·2-53·8=30·6| 15 | 61·2 | 38·5 | } |

+---------+---------------+--------------+-------+--------+--------+------------+

Estimated mean annual temperature of the summit of Mauna Loa, taking

that of the coast at 75°, would be 34° if the rate of increase was the

same as on Mount Pangerango in Java (1° per 328 feet).

The great daily range of temperature is one of the most striking

features of the climate of the summit of Mauna Loa. The extreme recorded

by me was 38·7°, whilst Wilkes registered as much as 42°. As on most

lofty mountains the dryness of the air, as indicated by the relative

humidity, was usually great. The average percentage during my stay

between 8 and 9 A.M. was 44, at midday 43, and between 5 and 6 P.M. 56.

This may be contrasted with 72, the average for the year at Honolulu. In

the tropics the mean for the year in the lower levels often rises to 80

and over; and it can scarcely be doubted that the Hawaiian climate is

generally drier than it was before the destruction of the forests. The

lowest relative humidity recorded by me on the summit of Mauna Loa was

20 per cent. Junghuhn on the summits of two mountains in Java, 10,500

and 11,500 feet in height, recorded percentages as low as 5 and 13.

Further details relating to this subject are given in Note 61. The

rainfall on the top of Mauna Loa is probably very slight. During my

sojourn rain was noted on six days, but on only two could it be

measured, and the total fall could not have amounted to over a third of

an inch.

The mean annual temperature of the great forest-zone at the elevations

where it displays the greatest luxuriance of growth on the island of

Hawaii, that is, between 4,000 and 6,000 feet, would be estimated at 63°

and 57° F., if we take the rate of decrease before employed of about

three degrees per 1,000 feet. But remembering the heavy rainfall in this

region and the usual occurrence of a protecting belt of cloud during the

day, this might seem to be too high. According, however, to a table

given by Mr. Jared G. Smith in his annual report of the Hawaii

Agricultural Experiment Station for 1902, the average temperature at

4,000 feet would be 65°. I cannot help thinking this is excessive as an

average for the island. In the latter part of May, 1897, the mean

temperature during my sojourn of twelve days at elevations between 6,000

and 6,700 feet around the slopes of Mauna Kea was 51·2°; whilst for

eight days in the first part of June in the same region the mean

temperature was 58·2° at an altitude of 4,000 to 4,300 feet.

It is possible, as I have pointed out on a later page, to recognise in

the different zones of vegetation the floras of a variety of latitudes;

and these zones are to a large extent controlled by temperature as well

as by other conditions. Thus the Fijian would be amongst familiar

vegetation on the lower slopes of Mauna Kea, whilst the Maori would be

at home halfway up the mountain-slopes, and the African from the upper

forests of Kilima Njaro and Ruwenzori would find in the higher levels

much to remind him of his native land.

The upper woods extend usually to 8,000 or 9,000 feet above the sea, and

vegetation of a scrubby character occurs as high generally as 10,000 or

11,000 feet. The highest regions present only a barren rocky waste.

THE RAINFALL.

_The Hawaiian Islands._—Although on account of the extensive deforesting

of the Hawaiian Islands since their discovery the contrast between this

group and that of Fiji is now, as regards rainfall, somewhat emphasised,

it is almost certain that in early times the contrast was much less

marked. In the lower levels the natives and sandal wood traders in the

past, and the agriculturists in the present, have accomplished much in

this direction. Between 1,000 and 3,000 feet, whole forests were in my

time disappearing under fire and axe for the coffee plantations. Above

those levels up to the higher limits of the woods, cattle were

destroying the forests in a wholesale fashion; whilst foreign insects

were proving themselves almost as great enemies to the vegetation. I

remember an enterprising agriculturist explaining to me how he cleared

the land of forest around his station. A large tract having been fenced

in, the cattle were introduced. After destroying the undergrowth and the

young trees, the animals attacked the bark of the trees, and in a year

or two, without fire or axe, the land was cleared. The consequence of

this unchecked destruction of the forests was in my time becoming only

too evident. When I passed through Ookala, on the Hamakua coast, at the

end of May, 1897, there was a water famine. Water was sold at a quarter

of a dollar a bucket, and the allowance for a family was three oil-cans

a week. Stealing water was a crime and punished by the plantation

authorities by dismissal or a five-dollar fine.

If we could look back for fifty or sixty years—I am now quoting from the

reports of Prof. Koebele and Dr. Stubbs—we should see large forests

where we now see barren slopes and plains. Originally forests covered

the upland plateaux and mountain slopes of all the islands. Now much of

the original forests has been removed, and large areas of naked soils

and bare rocks remain. The present forest area, writes Mr. Giffard, the

editor of the _Hawaiian Forester_ (August, 1904), is about 20 per cent.

of the islands, a small fraction of what it was a hundred years ago. It

is, however, very satisfactory to learn that American energy is now

combating this evil. Already in the January number of the same journal

is to be found a report by Mr. W. L. Hall, of the Bureau of Forestry, on

“The Forests of Hawaii”; and now, under the charge of Mr. Jared G.

Smith, institutions have been formed and experiment stations have been

established for “the intelligent and skilful cultivation of the soil.”

Hawaii owes much to the United States Department of Agriculture. May we

in England take the cue in the case of our own Crown colonies!

Under these circumstances the comparison of the present rainfall of

Hawaii must be carried out with discrimination. But it may be at once

observed that to make a contrast in detail between the rainfalls of

these three groups is quite beyond the province of this work; and this

remark applies also to the other observations on the climatic

conditions. I can only treat the subject in an illustrative fashion in

connection with the general subject of their floras.

Thanks to Professor Lyons, the Government meteorologist, the rainfall

has long been systematically investigated. It may be said to range

anywhere between 10 and 300 inches. As in most groups within the

trade-wind belts, there is a great contrast in the rainfall between the

weather and leeward sides of the islands, which is well exhibited in the

large island of Hawaii. Whilst in the Hilo district on the wet side of

the island the annual rainfall near the coast is about 120 inches, on

the Kona coast of the dry side of the island it may be anything between

20 and 50 inches and it may fall to less than 10. The effect of

elevation is, however, evident on both the weather and lee sides of the

island. Thus at a height of 1,650 feet in the Hilo district it is as

much as 180 inches, and at a greater elevation 210 inches. At a height

of about 1,600 feet at Kealakekua, on the dry side of the island the

average yearly rainfall, according to the results kindly supplied to me

by the Rev. S. H. Davis, was for the six years, 1891-6, 60 inches. On

the beach, as he says, it is “very much less,” probably not 30 inches.

Dr. Maxwell, in his report on “Irrigation in Hawaii,” mentions a

locality in Maui where the rainfall at the sea-shore was 28 inches, and

at a height of 2,800 feet up the mountain side as much as 179 inches. In

the region of the cloud-belt, which coincides with that of the

forest-zone on the slopes of the great mountains of Hawaii and extends

up from about 3,000 to 7,000 or 8,000 feet above the sea, the average

annual rainfall would probably be rarely under 200 inches, and in some

localities it might approach 300 inches. There are some particularly wet

mountains, and amongst these may be placed the high table-land of Kauai

(4,000 feet) and the flat summit of Mount Eeka (6,000 feet) in West

Maui. Here in a region almost of eternal mist we have developed a

special bog-flora.

Hillebrand describes the flat top of Mount Eeka as “wrapt in a cloud of

mist nearly the whole year.” Whilst descending this mountain I was

overtaken by the darkness at a little under 5,000 feet above the sea.

Through the night there was a continuous soft rain, or rather a heavy

wet mist, and I passed it under conditions suggestive of living in a

sponge. Everything was reeking with moisture. The air was saturated with

it, and water dripped from every leaf and branch, whilst the ground on

which I stood was soft and yielding and soaked with water like a sponge.

The surface was cut up by numerous narrow water-channels ten to twenty

feet deep and only a couple of feet wide, their very existence almost

concealed by ferns, whilst torrents rushed along at the bottom and kept

up a strange music through the night. This was the longest night I have

ever experienced, as my standing-ground was very limited, and with a

water-channel a foot or two away on either side I had to keep on my legs

until the dawn.

Above the cloud-belt, at elevations of 10,000 feet and over, the

rainfall is evidently very small. I have before remarked that during my

stay of twenty-three days (August 9-31) on the summit of Mauna Loa

(13,600 feet) the rain did not exceed one-third of an inch in amount. I

have by my side the report to the Weather Bureau, compiled by Prof.

Lyons, on the rainfall of this large island of Hawaii for the entire

month (August, 1897); and it enables one to make a comparison, in some

respects unique, of the distribution of the August rainfall on Mauna

Loa, from its base to its summit, where it occupies the breadth of the

island. Whilst on the east or wet side from the coast up to 1,500 feet

amounts ranging from 11 to 15 inches were measured, on the west or dry

side between one and two inches were registered at the coast, and 10

inches at Kealakekua, about 1,600 feet above the sea. But the level of

maximum precipitation would lie much further up the mountain slopes on

either side, probably at an altitude of 4,000 or 5,000 feet, and here

the rainfall for the month could not have been less in either case than

20 inches. Above this line of greatest rainfall the amount of

atmospheric precipitation would become less and less until beyond the

upper forest zone above 10,000 feet to the summit (13,600 feet) the

quantity would be very small; and judging from my observations, that

covered three-fourths of the month, the rainfall on the top of the

mountain for August would not have far exceeded half an inch.

The dry climate of the summits of Mauna Kea and Mauna Loa is reproduced

on the tops of the Java mountains and on the summits of the Owen Stanley

Range in New Guinea. Sir W. Macgregor found a fine and dry climate on

the top of the mountains last named, beyond the limits of the forests,

which extend to 12,000 feet above the sea. Below lay the cloud belt, a

zone of moss and fog, where at an elevation of 7,000 to 8,000 feet

everything was reeking with moisture (_Journ. Roy. Geogr. Soc._ 1890).

Observers at the coast often little imagine, when looking at a

cloud-concealed mountain peak, that although the cloud-belt from below

looks black and lowering and rain is falling heavily in the gloomy

forests, there is on the upper side a region of bright sunshine, and

that the peak stands out, unseen by them, above a sea of clouds

sparkling brilliantly in the sun and dazzling in their whiteness. It

will be seen from the table given in Note 61, that during my sojourn on

the summit of Mauna Loa the sky was cloudless or almost free from cloud

during nearly half the time. The mean cloudiness in the forenoon for

twenty-two days was 1·3 and for the afternoon 3·5, whilst the nights

were cloudless.

_The Rainfall of Fiji._—The rainfall of Fiji is known to be very large.

In illustration I will take Vanua Levu, the second largest island,

partly because of my familiar acquaintance with it, and partly because I

have at my disposal measurements for both the lee and weather sides of

the island—the first dry and characterised by a scanty and peculiar

vegetation, the second humid and densely forested. At Davutu, near the

sea-level on the weather or wet side of the island, the average yearly

fall for a period of sixteen years up to 1898 was 160 inches (these

observations were made in the grounds of the manager’s house and I am

indebted to Mr. Barratt for allowing me to inspect them). The

mountainous backbone of the island, which has an elevation ranging

usually from 2,000 to 3,000 feet, is generally in the rain-clouds.

During the months I was occupied in examining the geology of these

mountains, it was a common experience to be drenched to the skin all day

long, and I cannot doubt that the annual rainfall in the higher levels

must often reach 300 inches. Those familiar with the “sun-burnt” lands

or “talasinga” plains that mainly form the north or lee side of the

island, would expect a great difference in rainfall as compared with the

south or weather side. There is a marked difference, it is true, but it

is far less than we might have looked for. At Delanasau on the north

coast, less than a hundred feet above the sea, the mean rainfall for

seven years (1871-77), according to the observations of Mr Holmes, was

113 inches, and the range 80 to 159 inches (see Horne’s _Year in Fiji_).

In discussing the origin of the arid-looking plains on the north or lee

side of the island in Note 22, I have shown that the explanation is to

be found not so much in the rainfall as in the dryness of the air as

indicated by the relative humidity.

The rainfall varies greatly in and around Vanua Levu, but there is

little doubt that by far the greatest bulk of the rain is precipitated

on the upper weather slopes of the mountainous backbone of the island.

Taviuni, which lies off its weather coast, is probably the wettest among

the smaller islands of the group. In 1877, when 80 inches were recorded

by Mr. Holmes at Delanasau on the north side of Vanua Levu and 73 inches

at Levuka in the island of Ovalau, 251 inches were measured in Taviuni

at Ngara Walu 564 feet above the sea; and in 1875 the rainfall recorded

at Taviuni was 212 inches, and at Delanasau 126 inches (Horne).

Fortunately, the Fijian islands have not been long enough occupied by

the whites to produce much effect on the rainfall through the

destruction of the forests. A significant warning, however, has been

given in the vicinity of Levuka. The woods of the hills around the town,

as we learn from Mr. Horne, were cut down to prevent them from affording

shelter to the unfriendly natives of the interior, the result being to

reduce the number of rainy days in a few years from 256 to 149 per

annum.

_The Tahitian rainfall._—The annual rainfall of the coast districts of

Tahiti is placed at about 50 inches (_Encycl. Brit._ vol. 23); but, as

is observed by Nadeaud and Drake del Castillo, the rain-clouds gather

round the peaks, and the precipitation is much greater in the interior

than at the “littoral,” with a corresponding result in a striking

difference between the vegetation of the two regions. Probably,

therefore, the rainfall for the year on the wooded mountain slopes and

at the heads of valleys where the vegetation is most luxuriant would be

over 100, and perhaps as much as 150 inches in places. (The annual

rainfall in Rarotonga is, according to Cheeseman, about 90 inches.)

It is evident that in the three groups of Hawaii, Fiji, and Tahiti, the

rainfall varies greatly with situation and with elevation; but the

contrast is much greater in Hawaii than in Fiji. Thus there would be

scarcely any place on the lee side of Vanua Levu where the average

annual fall would be less than 80 or 90 inches, except perhaps in the

Undu Promontory, whilst on the lava-bound coast of the west or lee side

of Hawaii, it may be reduced to 20 inches and less. There is no doubt

that this was to some extent the case in pre-European times, since Fiji

must have possessed for ages, on the northern sides of the larger

islands, its arid “talasinga” or “sun-burnt” plains; and in the island

of Hawaii there must have always been vast, scantily vegetated lava

fields at the sea-border. It is probable, however, that it is in the

older islands of the Hawaiian group, those where the volcanic forces

have been long extinct, that the rainfall has been chiefly affected by

deforestation. Speaking generally, in pre-European times the climatic

conditions of the lower levels of the group, that is below 4,000 feet,

which are alone comparable with Fiji, were less contrasted with the

climatic conditions of the Fijian islands than they are at present. By

reason of their great elevation, the Hawaiian islands present a mountain

climate not found in Fiji, and scantily represented in Tahiti. It is,

therefore, in the flora of the Hawaiian uplands that we should expect to

find the great distinguishing feature between that group and Fiji.

_Summary of the Chapter._

(1) Whilst the winds and the currents have been working tranquilly

through the ages, bringing always the same vascular cryptogams and

shore-plants to the Pacific islands, the bird has ever been a disturbing

factor in the inland flora, and changes often of a revolutionary

character have taken place from time to time within the forest-zone.

(2) In the discussion of the inland plants of these islands, the Fijian,

Tahitian and Hawaiian areas are taken as centres of development and

dispersal, and as including the groups around.

(3) On account of the contrast in physical conditions presented by these

archipelagoes, differences with which some of the most distinctive

features of the floras are to be connected, a comparison of the islands

from this standpoint is first necessary.

(4) Since the largest islands of the Fijian and Hawaiian areas are from

five to ten times the size of Tahiti, the largest island of the Tahitian

region, we would expect to find in the two first-named groups a much

more varied flora.

(5) There are three huge mountain-masses in the Hawaiian group which

rise to between 10,000 and 14,000 feet, and there is in the aggregate a

large area elevated more than 4,000 feet above the sea. These elevated

regions are almost unrepresented in the southern groups, the Fijian

islands being only comparable with the lower levels of the Hawaiian

islands below 4,000 feet, and the same is true of all the groups with

the exception of a limited area in Tahiti, where the mountains reach a

height of 7,300 feet, and of the solitary peak of Savaii in Samoa, which

attains an altitude of 5,400 feet. Thus the conditions for a high-level

or mountain flora which exist in Hawaii are not to be found in Fiji, but

slightly in Samoa, and to a limited extent in Tahiti.

(6) From their position with regard to the equator and with reference to

the trade-winds a great contrast between the climates of these three

regions—the Fijian, the Tahitian, and the Hawaiian—is, as far as the

islands agree in elevation, not to be expected, and in fact does not

exist. The Fijian climate, however, is now warmer and more humid, and

the general rainfall is greater than in the case of Hawaii, but it is

probable that these differences were much less pronounced before the

destruction of the Hawaiian forests, which has been in progress since

the discovery of the group.

(7) Anywhere around the coasts of the larger Fijian islands we might

expect an annual rainfall of not less than 80 or 100 inches. In the

Hawaiian group the rainfall at the coast may be anything between 10 and

100 inches, but is generally less than 50 inches. In Tahiti, at the

coast, it is 50 inches. In all cases the rainfall increases greatly with

elevation. In the Fijian mountains the rainfall probably varies between

200 and 300 inches. In the Hawaiian forest-zone it would range probably

between 100 and 200 inches, though this is probably exceeded in a few

localities. In the Tahitian uplands it would doubtless exceed 100 inches

and approach 150 inches.

(8) Quite a different climate prevails on the lofty summits of Hawaii

13,000 to 14,000 feet above the sea. Here the snow lies in winter, and

the mean annual temperature is only a few degrees above the freezing

point, probably about 36° F. The difference between the mean summer and

winter temperatures is very small, and does not exceed five or six

degrees. Water freezes here during nearly every night of the year. The

daily variation of temperature is very large, the average being probably

about thirty degrees. Great dryness of the air prevails, the average

relative humidity in August, 1897, being about 43 per cent. There is but

little rain. The sun shines fiercely, and the sky is usually clear.

(9) All Pacific climates are represented in the Hawaiian mountains, that

of Fiji on the lower slopes, that of New Zealand half way up, and that

of the Antarctic islands on the summits.

(10) When contrasting the floras of Fiji, Tahiti, and Hawaii, it will be

necessary to restrict our comparison in the case of Hawaii to the lower

slopes below 4,000 or 5,000 feet; and we should expect the Hawaiian

mountain flora to be scantily represented in Tahiti, and scarcely at all

in Fiji and Samoa.

CHAPTER XX

THE EPOCHS IN THE FLORAL HISTORY OF THE PACIFIC ISLANDS

THE AGE OF FERNS

The epochs in the plant-stocking.—The age of ferns and lycopods.—The

relative proportion of vascular cryptogams in Hawaii, Fiji, and

Tahiti.—The large number of peculiar species in Hawaii.—The mountain

ferns of Hawaii.—The origin of peculiar species.—Dr. Hillebrand’s

views.—Their origin connected not with greater variety of climate in

Hawaii, but with isolation.—Summary.

_Introductory Remarks_

IN the endeavour to follow the various stages in the floral history of

the Pacific islands from the standpoint of plant-dispersal, a method is

here adopted which is not often employed. The usual mode of making a

general description of a flora is not intended to bring out its genesis

in point of time. We describe the result of a long series of changes

dating back to some unknown period, much as one might describe the

present condition of a people without reference to their history; and

for obvious reasons rarely is an effort made to differentiate the epochs

of the stocking of the region with its plants. The difficulties

investing such a task in the case of a region situated within a

continental area would be almost insuperable. With the oceanic groups of

the Pacific such difficulties, though still very numerous, would at all

events be fewer in number and less formidable in appearance.

Taking my cue from the well-known instance of Krakatoa, it is here

assumed that the earliest epoch is connected with the arrival of the

cryptogamic flora (ferns, mosses, lichens, &c.) through the agency of

the winds, and with the arrival of the littoral plants through the

agency of the currents. The next era is represented by the genera now

peculiar to each group, since it is implied that they have descended

from the earliest phanerogams that established themselves in the group.

The following epoch, which ends only with the arrival of man, is

characterised by the genera found outside the group; and here different

degrees of antiquity are indicated according as the genus is represented

wholly or in part by peculiar species, or contains only species found in

other regions. The following eight chapters will be devoted to the

development of the method here briefly indicated.

THE AGE OF FERNS.

It was established by Dr. Treub in the case of Krakatoa that ferns and

algæ formed the earliest vegetation of this island after it had been

completely stripped of all its plants in the great eruption of 1883. It

is, therefore, but natural that the vascular cryptogams should first be

dealt with in any discussion relating to the historical aspects of these

floras.

It has been before remarked that the epoch of ferns and lycopods, which

began with the earliest stage in the island’s floral history, may be

regarded as extending to our own day. It is thus implied that the

vascular cryptogams of those early times are yet brought there, and

that, alike with the littoral plants, these ferns and lycopods have

witnessed almost unchanged the great revolutions that have marked the

history of the inland flowering plants, more particularly those of the

forest flora. This, as I will show, is true in Hawaii, though only in a

partial sense in comparison with the other island-groups of Fiji and

Tahiti, since in Hawaii nearly half the ferns and lycopods are peculiar

to that group, whilst in Fiji and Tahiti not more than 8 or 9 per cent.

appear to be endemic. (Rarotonga, according to Cheeseman, possesses one

new species amongst its seventy-two ferns and lycopods, and probably in

this it is typical of the smaller elevated islands of Eastern

Polynesia.)

The large proportion of peculiar Hawaiian species is the central fact in

the distribution of vascular cryptogams in the Hawaiian, Fijian, and

Tahitian archipelagoes, and indeed in the Pacific islands; and it is

around this fact that much of the following discussion will lie. (For

the data relating to the Tahitian region, I have almost exclusively

followed Drake del Castillo.)

On looking at the table given below, it will be noticed that whilst

there are about the same number of species of ferns and lycopods in the

Tahitian and Hawaiian islands there are at least half as many again in

Fiji. When we reflect that the total areas of the Fijian and Hawaiian

groups are in each case about 7,000 square miles and that the extent of

the whole Tahitian region does not amount to 2,000 square miles, these

facts acquire a fresh significance. Ferns and lycopods might, therefore,

be expected to figure more largely in the Tahitian flora than in those

of Fiji and Hawaii; and this is indeed the case. When we examine the

relative proportion of the vascular cryptogams to the indigenous

flowering plants in each area we find that whilst in Hawaii they form

about 18 per cent. of the total flora and in Fiji not much more than

this (see Note 62), in Tahiti they constitute just a third. This excess

of vascular cryptogams is reflected in the flora of the outlying groups,

the proportion in Rarotonga being, according to Cheeseman, 30 per cent.

It is, therefore, evident that in comparison with the other groups

Tahiti possesses a marked preponderance in ferns and lycopods. In this

respect the Tahitian islands resemble those of Juan Fernandez, where

judging from the data relating to the indigenous flora given in

Hemsley’s _Botany of the Challenger Expedition_, the proportion of

vascular cryptogams amounts to between 30 and 38 per cent.

But it has been already implied that the proportion of endemic species

of ferns and lycopods is from four to five times as large in Hawaii as

it is in Tahiti or Fiji. In Hawaii, therefore, there has been a

production of many new species, whilst in Fiji and Tahiti there has been

a great rush of immigrants. “Formative energy” in Hawaii (to adopt an

expression of Dr. Hillebrand) and “active colonisation” in Fiji and

Tahiti, such would appear to be the most conspicuous features in the

history of the vascular cryptogams of these three archipelagoes.

In these floras it is, therefore, apparent that respecting the vascular

cryptogams the average number of species in a genus does not supply a

means of contrasting them. As indicated in the table, the fern and

lycopod floras of Fiji and Hawaii are similar in this respect. Yet in

each the average number of species to a genus has a separate

significance. A genus may acquire its species through immigration, or

they may arise from its formative energy within the particular area. The

first principle has been largely dominant in Fiji, the last in Hawaii,

and the resemblance between the average number of species in a genus in

these two groups is to a large extent accidental. Between the vascular

cryptogams of Fiji and Tahiti, however, such a comparison is legitimate;

and since the average formative energy is in these groups about the

same, the difference is to be attributed to a lessened number of

immigrants into the Tahitian area.

TABLE OF VASCULAR CRYPTOGAMS (FERNS AND LYCOPODS) IN THE GROUPS OF

TAHITI, HAWAII, AND FIJI. (See note 63.)

+--------------------+------+------+----+

+--------------------+------+------+----+

| Number of genera. | 38 | 29 | 40 |

+--------------------+------+------+----+

| Number of species. | 154 | 155 |237 |

+--------------------+------+------+----+

|Species to a genus. | 4·1 | 5·4 |5·9 |

+--------------------+------+------+----+

| Number of | 13 | 70 | 20 |

+--------------------+------+------+----+

| Percentage of | 8 | 45 | 8 |

+--------------------+------+------+----+

| and lycopods among | 33 | 18 | 21 |

+--------------------+------+------+----+

The results, so far mentioned, are in the main consistent with the

geographical position and the degree of isolation of these three areas.

From their proximity to the large continental islands of the Western

Pacific, the Fijian islands would have readily received a great number

of immigrants from the west, since the intervening sea is not over 500

miles in breadth. They lie in the track of the main line of migration

into and across the South Pacific, a track which has been followed by

flowering plants and animals as well as by aboriginal man. Assuming that

the migration of the vascular cryptogams extended from Fiji eastward to

Tahiti, fewer of the immigrants would reach the last-named group. Fewer

still would reach the Hawaiian islands, which excluding the groups of

low coral islands to the southward are cut off on all sides, whether

from the Fiji-Samoan and Tahitian areas, from the coasts of North

America, or from the regions north and west, by a breadth of ocean that

is never less than 1,500 miles.

That the main track of the ferns and lycopods across the South Pacific

to Tahiti has been eastward there can be little doubt. This is indicated

in the tables given by Drake del Castillo for Eastern Polynesia, and

also by an analysis I have prepared of the distributions that he gives

for the species of the Tahitian region (see Note 64). Out of the 154

species there are only two that belong exclusively to the American side

of the Pacific; whilst 58 are derived exclusively from the Asiatic side,

and mainly from Indo-Malaya. The drift of the ferns and lycopods

eastward from Fiji is also brought out in the number of Tahitian species

common to Hawaii and Fiji. Of these about 76 per cent. are common to

Fiji or to the groups around, and only 30 per cent. occur in Hawaii. The

Tahitian species found in Hawaii occur also in Fiji with the exception

of two or three mountain species which have doubtless failed to find a

suitable elevation in Fiji. These two or three mountain ferns and

lycopods are probably the only vascular cryptogams possessed in common

by Hawaii and Tahiti to the exclusion of other groups. (See Note 64.)

The prevailing Indo-Malayan origin of the ferns and lycopods of the

archipelagoes of the Fijian area (Fiji, Tonga, Samoa) is so well

established in the writings of Seemann, Baker, Hemsley, Christ, and

Burkill that there is no necessity to enter into details here. That the

stream of vascular cryptogams to Hawaii has proceeded mainly from the

Old World side of the Pacific is shown in the circumstance that of the

eighty and odd species found outside the group nearly half are from the

Asiatic side exclusively and only three from America alone, whilst about

a fourth occur in both continents, and a fourth are confined to

Polynesia. One point, says Dr. Hillebrand, comes out in strong relief,

and that is “the great number of ferns scattered over the long track

which leads from the Hawaiian islands through Polynesia and Malaysia to

the east coast of tropical Africa.” But he adds significantly that “it

cannot be inferred from this fact that all the species in question have

travelled eastward to find the terminus of their long migration on this

group, unless the principle be established, that the formative energy of

a species or genus be greatest at the circumference or farthest

extremity of its area” (p. 542).

Though evidently prepared to admit the general eastward trend of plants

in the Pacific, Dr. Hillebrand (p. xxviii) puts forward in the case of

the ferns the startling view that originally spores of a few simple

species have been diffused over various countries and that they have

there evolved on parallel lines “predetermined by the structure of the

original immigrant” a series of higher forms, so that the same form

might have been produced in two widely distant localities, as, for

instance, in Ceylon and Hawaii. The editor, Mr. W. F. Hillebrand, gives

good reasons for his belief that this does not represent the matured

opinion of the author. It is, however, worth noting in this connection

that Dr. Karl Mueller has advanced a similar view with respect to the

lower orders of plants. (See a translation of his paper in _Trans. and

Proc. N. Z. Inst._ Vol. 25.) Bearing in mind the known capacity of ferns

for dispersal by the winds, an hypothesis of this kind, even if

established, seems scarcely needed in the study of fern-dispersal.

It is probable that many of the ferns and lycopods reached Hawaii

directly and not through South Polynesia. The mountain-ferns of this

group could hardly have been received by that route, since, as is shown

below, they do not as a rule occur in that region.

Some other interesting relations present themselves in connection with

the Hawaiian ferns and lycopods when we consider the distribution of its

non-endemic species in the other two groups of Fiji and Tahiti. Out of

these species, some eighty in all, not more than half are common to all

three groups, and about two dozen have not been found either in Fiji or

in Tahiti. Of these last quite half are mountain species in Hawaii,

having their station at elevations exceeding those of the highest

districts of Fiji and of the several islands of the Tahitian area,

excepting the limited region comprised in the uplands of Tahiti itself.

A glance at the list, given in Note 65 of some of the mountain ferns of

Hawaii not recorded from Fiji and Tahiti will show that these species

are very widely distributed. Ferns and lycopods found in the Himalayas

and in the Andes meet on the higher slopes of the lofty mountains of

Hawaii and in no other of the less elevated island-groups of the open

Pacific. This distribution of the vascular cryptogams thus foreshadows a

principle that will come into prominence in the case of the flowering

plants, namely, that difference in elevation has been an important

factor in determining some of the contrasts between the Hawaiian,

Fijian, and Tahitian floras. The contrasts here implied are those

connected with the climatic conditions of station, since several plants

of temperate regions, such as Aspidium filix mas, Asplenium trichomanes,

Asplenium adiantum nigrum, &c., that are at home in the highlands of

Hawaii, do not occur in either Fiji or Tahiti. We can infer that widely

ranging ferns and lycopods have been dispersed over the oceanic groups

of the tropical Pacific with a fair degree of uniformity, and that any

marked contrasts in their distribution may be attributed to considerable

differences in the altitude of the islands.

In appreciating such a conclusion, and in dealing with apparent

exceptions to the rule, the relation between the vertical range of a

species and its lateral distribution has to be considered. We find, for

instance, that whilst the Common Bracken (Pteris aquilina) is a mountain

plant in Hawaii, it occurs also in Fiji and Tahiti. Since, however, it

is found all over the temperate and tropical regions, and has a vertical

range in Hawaii of from 800 to 8,000 feet, any difficulty in this

respect is thus explained. Aspidium aculeatum, a characteristic fern of

temperate latitudes, seems at first to present a difficulty, which,

however, proves to be more apparent than real. Whilst it has been

recorded from Hawaii at heights of 6,000 to 9,000 feet, and from Tahiti

at 4,000 feet, it has also been found in Fiji and Samoa; but since it

was not collected by Seemann in Fiji, it can scarcely be common, and

Horne seems only to have obtained it from the tops of mountains in Vanua

Levu at an elevation of 1,800 feet.

Up to this point the non-endemic ferns and lycopods have been chiefly

discussed. We will now briefly deal with the probable cause of the

relative preponderance of peculiar or endemic species in Hawaii as

contrasted with Fiji and Tahiti. In this respect the Hawaiian islands,

as remarked at the commencement of this chapter, come into sharp

contrast with the other two groups; but it would seem that the

differentiation has rarely acquired a generic value (see Note 66). In

this respect the age of ferns is markedly distinguished from the

succeeding era, the age of the arborescent Compositæ and of

Tree-Lobelias, to which a large number of peculiar genera belong. This,

according to my view, is to be attributed to the circumstance that

whilst the dispersion of spores by the wind is probably as active in our

own time as it was in the earliest stage of the floral history of

Hawaii, the dispersion of seeds by birds, to which the flowering plants

in the main originally owe their presence in this group, has been

greatly influenced by the various changes that have affected the

migration of birds over the Pacific, a subject discussed in later pages.

Respecting the origin of the species of ferns and lycopods peculiar to

Hawaii, it is first of importance to quote the remarks of Dr. Hillebrand

on the subject. Speaking of the whole flora (p. xxv), but evidently with

the ferns more especially in his mind, he says:—“Nature here luxuriates

in formative energy. Is it because the islands offer a great range of

conditions of life? Or is it because the leading genera are in their age

of manhood, of greatest vigour? Or is it because the number of types

which here come into play is limited, and, therefore, the area offered

to their development comparatively great and varied?” It is deeply to be

regretted that sickness and death intervened before the author was able

to give to the world his matured views on the very important points here

raised. Yet they are much the same questions that man is ever putting to

the life around him. There is the same querulous note that we find in

all, the question that begins, the question that ends, and the reply

that never comes.

“The evolution theory (writes Dr. Hillebrand, p. xxix) could hardly find

a more favourable field for observation than an isolated island-group in

mid-ocean, large enough to have produced a number of original forms, and

at the same time so diversified in conditions of temperature, humidity,

and atmospheric currents as to admit an extraordinary development in

nearly every direction of vegetable morphology, uninfluenced by

intercrossing with foreign elements.” Isolation thus admittedly offers

the preliminary determining or favouring conditions. This is directly

indicated by the fact that Hawaii possesses fewer genera of ferns and

lycopods than either Fiji or Tahiti, notwithstanding that it has the

same area as Fiji, and is in extent three or four times the size of the

whole Tahitian area. One effect of isolation in Hawaii has, therefore,

been greater room for the development of new forms. It has, however,

already been remarked that the islands of the Fijian area are much less

isolated than those of the Hawaiian group, and that in consequence the

free immigration possible in the one group has been checked in the

other. Fiji possesses in respect to vascular cryptogams at least half as

many species again as Hawaii, but Hawaii has three or four times the

number of peculiar species. Yet before this great contrast can be

ascribed to different degrees of isolation, it is necessary to exclude

another possible cause presented by the greater range of life-conditions

in Hawaii. It is possible that all the Hawaiian peculiar species may

belong to the higher levels, elevations, as before shown, not

represented in the Fijian islands, which correspond only to the lowlands

of Hawaii, that is, to levels below 4,000 feet. If this is the case, the

contrast between Fiji and Hawaii would be connected mainly with a

difference in life-conditions, and, however potent the isolating

influences might have been in Hawaii, they could hardly have been

concerned with this striking difference.

In order to determine this point, I went carefully through the account

given by Hillebrand of the Hawaiian ferns and lycopods, noting the

altitudes there given, and making use of the maps and of my own local

knowledge of the islands of Oahu and Hawaii, where the elevation is

neither directly nor indirectly implied. As a result, I found that out

of sixty-six endemic species available for my purpose, forty-seven had

their stations at levels below 4,000 feet, that is in the region

corresponding to Fiji, and nineteen at elevations exceeding this height.

This, however, did not finally decide the question, since the proportion

of endemic species may be much smaller in the region below 4,000 feet

than in that above it. I, therefore, went over the ground again, and

found, as shown in the table below, that the percentages of peculiar

species amongst the total available for my use were not very far apart,

58 per cent. for the upper region and 43 per cent. for the lower region.

Distribution of the Hawaiian ferns and lycopods above and below 4,000

feet.

+------------------------+-------+--------+----------------+

+------------------------+-------+--------+----------------+

|Species below 4,000 feet| 110 | 47 | 43 |

+------------------------+-------+--------+----------------+

|Species above 4,000 feet| 33 | 19 | 58 |

+------------------------+-------+--------+----------------+

From the above it would appear that although the process of

species-production in the Hawaiian islands has seemingly been rather

more active above than below 4,000 feet, if we were to compare the

entire vascular cryptogamic flora of Fiji with that of the corresponding

lower levels of the Hawaiian group we should obtain much the same

contrast in the proportion of peculiar species that we obtained when

comparing all the ferns and lycopods of both groups. In other words, if

we were to restrict our comparison with Fiji, and I may add Tahiti, to

that lower portion of Hawaii that corresponds in elevation, we should

not get results very different from those to be obtained by including

the Hawaiian upland regions as well.

We are, I think, on these grounds justified in assuming that the

relatively great development of new species of ferns and lycopods in

Hawaii as contrasted with Fiji is not to be connected with the greater

elevation of those islands. The only thing that we have been able to

associate with the greater altitude of the Hawaiian Islands, and the

consequent greater range of climatic conditions, when contrasting the

Fijian and Hawaiian vascular cryptogams, is the occurrence of a number

of peculiar mountain species and of wide-ranging temperate species that

are found in the uplands of Hawaii, but not in the less elevated islands

of Fiji.

On the whole, therefore, it is to be inferred that the greater display

of formative power among the ferns and lycopods of the Hawaiian Islands

is in great part to be associated with the isolation of this group as

compared with those of Fiji and Tahiti. The indications supplied by the

vascular cryptogams resemble in kind those we shall obtain from the

study of the flowering plants, but there is this important distinction.

In formative power, as shown in the development of new specific and

generic types, the Hawaiian vascular cryptogams are far exceeded by the

flowering plants where the proportion of endemic species amounts to 80

per cent. We have no reason to believe that the winds, to which the

ferns and lycopods chiefly owe their dispersal, are less effective now

in carrying their spores than they were in the earliest era of the

floral history of Hawaii or in the intervening periods. In the course of

ages the winds have been more uniform in their action as

plant-dispersers even than the currents, and certainly far more than

birds.

On the other hand, in the case of the Hawaiian flowering plants that

depend on the varying influence of the migrant bird, the agency of

dispersal has often been suspended altogether, and far greater

differentiation or departure from the original type has resulted, the

amount of change often reaching to the value of a generic distinction.

It is a question, however, whether the isolation of the Hawaiian Islands

is to be entirely connected with their mid-oceanic position. It will be

shown in Chapter XXXIII. that effects almost as great have been produced

in continental regions and in continental islands, and that the isolated

situation of Hawaii has not induced but has intensified these results.

In the later eras of plant-life a process of segregation has been ever

active throughout the tropical world whether in the case of an elevated

oceanic island or of a mid-continental mountain.

The following are some of the principal points that have been emphasised

in the foregoing discussion of the ferns and lycopods of the Hawaiian,

Fijian, and Tahitian Islands:—

(_a_) In all three groups the vascular cryptogams (ferns and lycopods)

have been largely supplied from the warmer regions of the Old World. But

whilst in the South Pacific the migration has been mainly from Fiji

eastward to Tahiti, it is probable that Hawaii in the North Pacific has

been in part independently stocked.

(_b_) Whilst in Hawaii many peculiar species of ferns and lycopods have

been developed, in Fiji and Tahiti there have been comparatively few.

(_c_) Whilst there has been more or less free immigration into Fiji and

Tahiti there has been comparative isolation in Hawaii. Though the areas

of the Fijian and Hawaiian archipelagoes are about the same, Fiji

possesses at least half as many species again as Hawaii; but Hawaii owns

three or four times the number of peculiar species.

(_d_) Though the land-area of the Tahitian region does not exceed a

fourth part of that of Hawaii, it has the same number of species. The

Tahitian islands therefore display a predominance of ferns and lycopods.

(_e_) The non-effective influence of the greater elevation of the

Hawaiian Islands on its preponderance of peculiar species is shown by

comparing all the ferns and lycopods of the Fijian and Tahitian Islands

with those of the corresponding lower levels of the Hawaiian Islands,

when we find much the same contrast exhibited in the number of peculiar

species.

(_f_) Whilst a large proportion of the ferns and lycopods are common to

all three groups, Hawaii possesses a number of mountain species, widely

distributed in temperate regions and on the higher levels of mountainous

areas in the tropics, that are not found either in Fiji or in Tahiti.

Their absence from these two groups is due to the insufficient elevation

of the islands and to the non-existence there of extensive areas of any

altitude.

(_g_) The agency of the winds in dispersing the spores of ferns and

lycopods has been relatively uniform through the ages when compared with

the varying agency of the migrant bird, to which the flowering plants

mainly owe their distribution. Thus it is that in the Pacific islands

the vascular cryptogams have experienced much less differentiation than

the flowering plants, though as a rule far older denizens of the

islands. Yet we cannot doubt that the same principle has been at work in

both cases, the difference arising in the instance of the flowering

plants from the interrupted and often suspended agency of birds in the

work of dispersal.

(_h_) It is a question whether there is not something more concerned in

the isolation of the Hawaiian group than its mid-oceanic position, since

effects almost as great have been produced in continental regions.

CHAPTER XXI

THE ERAS OF THE FLOWERING PLANTS

THE AGE OF COMPOSITÆ.

The islands of the tropical Pacific as the homes of new genera and new

species.—The significance of a large endemic element.—Synopsis of the

eras.—The era of endemic genera.—The endemic genera of

Compositæ.—Their affinities and mode of dispersal.—The mystery of the

suspension of the dispersing agencies.—Mr. Bentham’s views.—The

remnant of an ancient Composite flora in the tropical Pacific.—The

dispersion of the Compositæ antedates the emergence of the

island-groups of the Fijian region at the close of the Tertiary

period.—Summary.

_The Endemism of the Pacific Island Floras._

AS far as the production of new species is concerned, the Hawaiian group

presents the same contrast with the Fijian and Tahitian groups in

respect of the flowering plants that it does as regards the ferns and

lycopods. The proportion of endemic species, after excluding all

introduced plants, is in Hawaii 80 per cent., in Fiji about 50 per

cent., and in Tahiti 35 per cent. (see Table A). The same contrast is

also displayed in the number of peculiar genera. In Hawaii there are,

according to Dr. Hillebrand, 37 or 38, and in Fiji Dr. Seemann

discovered 16; whilst, as we learn from Drake del Castillo, there are

only 3 or 4 in the Tahitian Islands. (As will be pointed out later on,

these numbers for Fiji and Hawaii have to be reduced, but the general

inference to be drawn from them is not materially affected; see Table

B.)

But if we look at the accompanying table (Table B) we notice that the

flora of Hawaii is sharply contrasted with those of Fiji and Tahiti not

only in the large proportion of endemic genera, but also in the large

number of non-endemic genera with peculiar species, and in the small

proportion of genera possessing no peculiar species. There is an endemic

element of greater or less degree in about 70 per cent. of the Hawaiian

genera, whilst in Fiji only about 53 per cent. and in Tahiti as few as

34 per cent. of the genera contain to a varying extent peculiar species.

Another feature brought out in this table is the relative poverty of

genera in the Hawaiian Islands. Fiji, though about the same size as

Hawaii, contains nearly half as many genera again, whilst the islands of

the Tahitian region, which in the aggregate amount to only one-third or

one-fourth of the area of the islands of Hawaii, possess nearly as many

genera.

TABLE A (FLOWERING PLANTS).

_Proportions of Endemic Species in the Hawaiian, Fijian, and Tahitian

floras, with those

for Samoa, Tonga, and Rarotonga added._

+---------+------------------+----------------+----------------+

+---------+------------------+----------------+----------------+

| Hawaii | 686 | 546 | 80 |

| | | | |

| Fiji | {S. 617 | {288 | {47 |

| | {H.1086 | {620 | {57 |

| | | | |

| Tahiti | 315 | 112 | 35 |

+---------+------------------+----------------+----------------+

| Samoa | 326 | 110 | 34 |

| | | | |

| Tonga | 285 | 17 | 6 |

| | | | |

|Rarotonga| 140 | 17 | 12 |

+---------+------------------+----------------+----------------+

_Remarks._—The materials for this table have been obtained from the

works of Hillebrand for Hawaii, Seemann and Horne for Fiji, Drake del

Castillo for Tahiti, Reinecke for Samoa, Hemsley and Burkill for Tonga,

and Cheeseman for Rarotonga. The two estimates for Fiji are marked S.

for Seemann and H. for Horne, the last being a rough preliminary

computation made by Horne himself.

The results given are only to be considered as approximations liable to

emendation, but as regards the proportion of endemic species in the

several groups they no doubt illustrate fairly well the relative degree

of endemism in the various archipelagoes. The results for Samoa, Tonga,

and Rarotonga are merely added in order to enable a comparison to be

made with sub-groups of a region and with solitary islands, the

Hawaiian, Fijian, and Tahitian groups being regarded as the three

principal centres of plant-life in the open Pacific.

All plants introduced by the aborigines and the white man are excluded.

In so doing, I have mainly followed Seemann, a safe guide in all matters

relating to weeds and to cultivated plants. The flora of a Pacific

island thus treated undergoes serious diminution in its extent. In the

case of the Rarotonga flora, for example, which according to Cheeseman

includes about 260 flowering plants, the number of truly indigenous

plants, in the sense here implied, is only 140. Though this is an

extreme case, it will serve to illustrate the principle here followed.

TABLE B (FLOWERING PLANTS).

_Comparison of the Hawaiian, Fijian, and Tahitian genera._ (_All genera

containing

introduced plants entirely are excluded._)

+----------+------------------------------------------+---------+-----------+

| +------------+---------------+-------------+ | |

| | | not. | | | |

+----------+------------+---------------+-------------+---------+-----------+

|Hawaii | 70(31)| 30(13)| 95(43)| 28(13)| 223(100)|

| | | | | | |

|Fiji {| S. 150(47)| S. 74(23)| S. 87(27)| S. 10(3)|S. 321(100)|

| {| H. 162(47)| H. 80(23)| H. 94(27)| H. 10(3)|H. 346(100)|

| | | | | | |

|Tahiti | 125(66)| 21(11)| 40(21)| 4(2)| 190(100)|

+----------+------------+---------------+-------------+---------+-----------+

_Remarks._—The figures in brackets are percentages. S. = Seemann, H. =

Horne and Seemann.

In the construction of this table, Hillebrand, Seemann, and Drake del

Castillo have been mainly followed, except with regard to the endemic

genera for Hawaii and Fiji. In this respect the _Index Kewensis_ has

been largely consulted as well as Engler’s publications, as indicated in

the text. Hillebrand’s total of nearly forty Hawaiian peculiar genera

and Seemann’s total of sixteen for Fiji have thus been considerably

reduced. The two results given for Fiji are those of Seemann alone and

with Horne superadded. Horne discovered, according to Hemsley, no new

genera, but several genera from outside regions were added to the Fijian

flora. Taking them as twenty-five (two-thirds of his own computation), I

have apportioned them as in Seemann’s results. The Tahitian region here

includes Eastern Polynesia.

It is necessary before proceeding further to obtain a correct idea of

the significance of a large endemic element in the phanerogamic flora of

a Pacific archipelago. We have therefore at the outset to inquire

whether it is indicative of isolation or of antiquity. If the number of

peculiar genera is to be regarded as the test of the relative antiquity

of different Pacific floras and, by implication, of the islands to which

they belong, these three groups, as shown in Table B, would arrange

themselves in the following order, namely, Hawaii, Fiji, Tahiti. This

test might be reliable if the several groups were in the same condition

of isolation. Since, however, as we have previously seen, the Fijian

Islands still enjoy a fairly free communication with the islands

westward, whilst the Hawaiian group is largely cut off, it is apparent

that the tendency to generic differentiation in Fiji might have been

often swamped by immigration, and that Fiji with its much smaller number

of endemic genera may even be older than Hawaii. This objection does not

apply quite as forcibly to a comparison between Hawaii and Tahiti, yet

for reasons before given it may be regarded as sufficient to negative

any inferences concerned with relative antiquity.

On account, therefore, of the great differences in the degree of

isolation of these three groups, we cannot be guided in our estimation

of the relative antiquity of their floras by their number of peculiar

genera. With the evidence at our disposal we are compelled to accept the

view, which indeed a single glance at a map would suggest, that the

number or proportion of endemic genera is to be connected with the

degree of isolation. Whether a parallelism can be traced in the original

stocking of these groups with their earliest flowering-plants is a

matter that can only be elucidated by a further analysis of the peculiar

genera.

SYNOPSIS OF THE ERAS OF THE FLOWERING PLANTS IN THE TROPICAL PACIFIC.

A. _The Era of the Endemic Genera._—Mostly American in their affinities.

Represented particularly by Compositæ and Lobeliaceæ.

B. _The Era of Non-Endemic Genera._

(1) The mountain genera, either cosmopolitan in temperate latitudes or

derived from the New Zealand or the Antarctic flora. Mostly

represented in Hawaii.

(2) The genera forming the low-level flora of Hawaii below 4,000 or

5,000 feet and composing almost the entire floras of the Fijian and

Tahitian regions. Predominantly Indo-Malayan.

(_a_) The age of general dispersal over the tropical Pacific, the

genera with only peculiar species being first treated, and afterwards

those possessing a non-endemic element.

(_b_) The age of local dispersal over the tropical Pacific.

THE FIRST ERA OF THE FLOWERING PLANTS, BEING THE AGE OF THE ENDEMIC

GENERA.

With the above preliminary remarks I pass on to the next stage in the

history of the stocking of these islands with their plants. The age of

the ferns and lycopods is left behind, and it is assumed that the next

era is mainly indicated by those genera of phanerogams that are now

peculiar to their respective groups. In this connection by far the most

interesting of the three regions, the Hawaiian, the Tahitian or East

Polynesian, and the Fijian, is that of Hawaii, which, as before

observed, is distinguished from the groups of the Fijian and Tahitian

regions, or, in other words, from all the oceanic archipelagoes of the

tropical Pacific, by its large number of endemic genera.

Peculiar genera of shrubby and arborescent Compositæ and of arborescent

Lobeliaceæ form the most striking characteristics of the endemic genera,

and therefore of the ancient flora of Hawaii. It is in this connection

of singular interest to remark that of the three endemic genera of the

Tahitian flora one is an arborescent genus of the Compositæ, and the

other two are shrubby genera of the Lobeliaceæ. There are, therefore,

indications here of an ancient insular flora of the Pacific,

characterised mainly by the prevalence of Compositæ and Lobeliaceæ. It

is, however, remarkable that not only are no endemic genera of these

orders known from Fiji or from the adjacent groups of Samoa and Tonga,

but that the Lobeliaceæ are not represented at all, whilst amongst the

Fijian Compositæ, with the exception of Lagenophora, the genera display

no endemic element as far as the data at my disposal indicate.

The problem we are brought face to face with is clearly stated by Mr.

Hemsley in the _Introduction to the Botany of the Challenger Expedition_

(p. 68). “In Polynesia as elsewhere,” he remarks, “the Compositæ more

particularly are perplexing to the botanical geographer, for although

they have their greatest affinities in America, as well as the

sub-arboreous Lobeliaceæ, so numerous in the Sandwich Islands, yet the

bulk of the vegetation seems to have been derived from the

Australo-Asiatic region.”

In attempting to approach this problem I do so from the standpoint of

dispersal. There are so many intricate questions bound up with the

systematic position of these genera that in dealing with them the

student of plant-distribution would require the capacities and

opportunities of the eminent botanist who dealt with the distribution of

ten thousand species of Compositæ. On such ground, therefore, and only

under the guidance of others, I will lightly tread.

THE ENDEMIC GENERA OF COMPOSITÆ.

On account of their endemic character the peculiar genera of Compositæ

are regarded as belonging to the oldest era of the flowering plants of

the island-groups lying in the tropical latitudes of the open Pacific.

This is the view of Bentham, but it is, of course, the opinion that most

botanists would arrive at with the facts before them. With the exception

of the solitary Tahitian genus Fitchia, they are all restricted to the

Hawaiian Islands, and nearly all are either shrubby or arborescent, the

greatest height of 25 to 30 feet being attained in the Tahitian genus

and in Hesperomannia of Hawaii.

Nine Hawaiian genera are included in this era, though, strictly

speaking, we ought only to concern ourselves with the six genera, Remya,

Argyroxiphium, Wilkesia, Dubautia, Raillardia, and Hesperomannia, since

the other three, Tetramolopium, Lipochæta, and Campylotheca, are only on

the borderland of generic distinction. It is, however, necessary that we

should include these three genera in our treatment of the Hawaiian

endemic genera, more especially because they appear to have been the

last arrivals of the early Compositæ. They still display, as shown

below, a very suggestive connection with the land of their birth, a

circumstance that is of much importance in finally determining the

source of the other strictly endemic genera, where the links with their

original homes have been in most cases largely severed.

It would, however, be quite out of place here to enter into any details

into the affinities of these Hawaiian genera of Compositæ, and I will

limit myself here to such general conclusions as may be derived from the

pages of Bentham, Hillebrand, Hemsley, and other writers, and such as

are in accordance with the facts of distribution given in the _Index

Kewensis_. Most ancient of all are the genera Remya, Argyroxiphium,

Wilkesia, and Hesperomannia, which, although belonging to tribes that

only occur on the American continent, as in the Mexican region, stand

quite isolated, and, as Dr. Hillebrand remarks, probably belong to the

oldest denizens of the Hawaiian Islands. It is noteworthy that these

four ancient genera only contain two species apiece, a circumstance that

favours their priority in point of age.

The American affinities, however, are not always of the character that

we might have expected. Thus, it was remarked by Mr. Bentham that

although the tribe Mutisiaceæ attains a great development in South

America, and especially in Chile, its only representative in the Pacific

islands is the very rare arboreous Hesperomannia of Hawaii.

Rather less isolated in character, and we would presume therefore of

somewhat less antiquity, are the two closely allied genera of Raillardia

and Dubautia, which have a close relative in Raillardella of the Sierra

Nevada in California. Then we come to the three genera, Tetramolopium,

Lipochæta, and Campylotheca, that, being still in touch with the world

outside, may be regarded as the latest arrivals of the early genera of

the Compositæ. Tetramolopium, concerning which botanists were unable to

agree, would seem, according to the _Index Kewensis_, to possess Mexican

and Ecuadorian as well as Hawaiian species. Lipochæta, nearly related to

other American genera, contains a dozen species, of which eleven are

found only in Hawaii, whilst the twelfth occurs, according to the _Index

Kewensis_, in California, and, according to Dr. Hillebrand, in the

Galapagos group. Of the generic value of Campylotheca there seems a

doubt, and its distinctness is scarcely recognised in the _Index

Kewensis_. It is, however, closely allied to Coreopsis, an American

genus represented, according to Drake del Castillo, in the Marquesas.

In the Tahitian region, that is to say in Eastern Polynesia, the genus

Fitchia alone belongs to the early age of the Compositæ, so

characteristic of Hawaii. Indications of the former widespread range of

the genus over this region of the South Pacific are afforded by its

being now represented by two species in Tahiti and by one species in

Rarotonga, localities nearly 700 miles apart. It was thus regarded by

Bentham, who saw in it a solitary remnant of the ancient South Pacific

flora. Like the Hawaiian genera, as shown below, it is often restricted

to the higher levels. Botanists differ about its affinities, and a

discussion of the subject will be found on pages 20 and 66 of the

_Introduction to the Botany of the Challenger Expedition_.

The restriction of these ancient genera of the Polynesian Compositæ to

the upland regions is of some interest. “The preponderance of Compositæ

among the high-level plants obtains almost throughout the world.” This

observation was made by Mr. Hemsley in connection with the flora of the

highlands of Tibet (_Journ. Linn. Soc. Bot._ vol. 35, 1902), where the

Compositæ constitute about 19 per cent. of the flowering plants; and I

may remark in passing that, according to Mr. Ball, one of the most

conspicuous elements in point of frequency in the higher flora of the

Great Atlas is presented by the Compositæ which make up between 12 and

13 per cent. of the whole flora (Hooker and Ball’s _Marocco and the

Great Atlas_). This feature of alpine floras is brought into great

prominence in Schimper’s recent book on Plant Geography.

Some of the most lasting reminiscences that the naturalist will bear

away with him from the highlands of Hawaii are connected with the

Compositæ. Those who have ascended the mountains of Mauna Kea and Mauna

Loa, will remember that amongst the last plants occurring above the

forest zone, and scattered about on the ancient lava fields at

elevations exceeding 10,000 feet above the sea, are species of

Raillardia and the beautiful “Ahinahina” (Argyroxiphium). It is,

however, in the open, scantily wooded region, elevated 6,000 to 9,000

feet, and lying between the true forest zone below and the bare lava

slopes above, that the shrubby and arborescent Compositæ of the large

island of Hawaii are most at home. Such regions, as Hillebrand well

describes (p. xxiv), are characterised by stunted trees, chiefly

Sophora, Cyathodes, Myoporum, and others, associated with arborescent

Raillardiæ of the order of Compositæ. Between them luxuriate other

shrubby Compositæ of the genera Raillardia, Dubautia, Campylotheca, and

Artemisia, together with Strawberries, Raspberries, and species of

Vaccinium.

Botanists have not given us much account of the associates of the

interesting genus Fitchia on the uplands of Tahiti. We learn, however,

from Nadeaud that in his time these Composite trees and shrubs were

spread over the higher region of the island of Tahiti above 800 and

1,000 metres. Cheeseman, to whom we are indebted for the discovery and

the description of the Rarotongan species, tells us that this tree,

which attains a height of 25 feet in the sheltered valleys, and is much

dwarfed on the exposed ridges and hill-tops, often forms the greater

part of the forest above 500 feet, and reaches the highest peaks of the

island (2,250 feet).

In discussing the probable mode of dispersal of these early Composite

plants of the Pacific we shall be treading on somewhat debatable ground.

We will, however, point out that the mere possession of structures that

could be utilised for dispersal of the seeds is not the only important

question here involved. If we could demonstrate that all these genera

possess exceptional capacities for distribution over the ocean, we

should prove too much, since the process has been in the main suspended

for ages. If, on the other side, it could be shown that their fruits are

not at all suited for such dispersal, we should prove too little, since

the ancestors of these genera must have been transported to these

islands in some fashion or other. This clearly indicates that other

important factors have also come into play in determining the

distribution of the early Compositæ of the Pacific islands.

It was long ago pointed out by De Candolle that the possession of a

pappus does not, as a rule, increase the area of a Composite plant,

although as regards hooks and barbed appendages, such as occur in

Bidens, the greater areas of the plants thus provided may be, as he

thought, in some measure explained. Even in respect to hooks and barbs

it would be easy to point to cases where, as Bentham remarks, unusual

powers of adherence are by no means indicative of wide dispersal in all

cases. In any event it will be also incumbent on us to explain why these

genera no longer possess facilities for distribution. This suspension of

the means of dispersal is not, however, peculiar to the age of the

endemic genera of the Pacific islands. It is a character but in a less

degree of the succeeding age, the age of genera found outside the group,

but represented within it by endemic species; and from this we may

suspect that we have had in operation in the Pacific an influence,

far-reaching both in time and space, to which the agencies of dispersal

have been compelled to adapt themselves, an influence which has acted as

a distributor of the distributing agencies.

Coming to the fitness for dispersal of the achenes of the early

Composite genera of the Pacific islands, it will be assumed that they

have been, as a general rule, transported in birds’ plumage. The fruits

are usually 2·5 to 12 millimetres (1/16 to 1/2 inch) in length, and are

provided either with a pappus of soft or stiff bristles, or with awns or

teeth, but these appendages vary much in size in the different genera

and in different species of the same genus. The instance of Lipochæta is

especially significant as indicating the alterations which the

appendages of the achene may have undergone in the cases of other

genera. With most species there are usually two or three teeth or short

awns, but in some species these are obsolete, and in others they are

long and stout.

Bearing these facts in mind we should hesitate to rely too much on the

present condition of the achenes in the other genera as an indication of

the fitness for dispersal of the fruits of their ancestors. In one

genus, Campylotheca, which may be regarded as among the youngest of the

genera, the achenes are provided with barbed or hooked awns which cause

them to adhere as tenaciously to one’s clothes as in the case of those

of Bidens, an allied genus. In Fitchia, the Tahitian genus, which may be

looked upon as one of the oldest of the Pacific genera of Compositæ, the

achene is furnished with two long awns or setæ, which, as Drake del

Castillo observes, recall those of Bidens. The achenes of the other

Hawaiian genera, as regards their fitness for dispersal in plumage, may

be said to give less definite indications. In some, as in Dubautia and

Raillardia, there is a typical pappus of ten to twenty long hair-like

bristles. In others again, as in Wilkesia and Argyroxiphium, the pappus

is much reduced, and in some species of Lipochæta it is, as above

remarked, quite obsolete.

The chances of the achenes of the parent plants having in some cases

been originally transported to the islands in the plumage of birds would

be increased by a bird making its nest of the plant-materials or amongst

the plants themselves, or by its pecking at the fruit-heads. In our own

time different species of the grouse family on the slopes of the

Californian and Columbian mountains make their nests on the ground under

the shade of Artemisia bushes and find a portion of their sustenance in

their fruits. Artemisias also form one of the features of the vegetation

of the Hawaiian uplands; but since they present only specific

differentiation they are referred to a later era. Yet it will be on the

slopes of the Rocky Mountains and of the Californian Sierra Nevada,

amongst the “sage-brush” and the grouse, that we may have to stand when

we look in thought across the Pacific towards far distant Hawaii and ask

ourselves whence came its tree-like Raillardias, its shrubby Dubautias,

its tall Wilkesias, and the silvery Ahinahinas (Argyroxiphium).

It is possible that in some genera the achenes have, or had, a means of

adhering to plumage through a “sticky” secretion, such as is sometimes

found with Lagenophora, an Hawaiian genus of the next era, and also with

the weed-plant Adenostemma viscosum; but this is a point that has not

yet been investigated. Nor can we altogether exclude the chance of the

achenes having in some cases been transported unharmed to Hawaii in a

bird’s stomach. The possibility of this has been above implied in the

case of Artemisia; and it is pointed out in Chapter XXXIII. that pigeons

in Hawaii feed sometimes on the achenes of Compositæ. The Hawaiian goose

(Bernicla sandwicensis) lives, according to Mr. Dole, on Sonchus asper,

an introduced plant, as well as on berries (Wilson’s _Aves

Hawaiiensis_). There are numerous references of this nature in books

about birds, and it should always be remembered that birds in pecking at

the fruit-heads scatter the seeds on their feathers. (See Note 67.)

From the foregoing remarks it may, I think, be inferred that the achenes

of the ancestors of the original Composite genera of the Pacific islands

were in all probability not unfitted for transport by birds, more

especially in their plumage. Some of my readers, however, may express a

doubt as to whether birds likely to disperse seeds would be found in any

numbers at the great heights where some of the continental Compositæ

occur. But it is well known that birds of the grouse and partridge

family frequent high levels in continental regions over much of the

globe. Arborescent Compositæ are found at heights of 10,000 to 14,000

feet on the mountains of Central Africa; and it should be noticed that

Sir Harry Johnston observed “francolins” on the slopes of Ruwenzori up

to 13,000 feet (_Uganda Protectorate_, vol. 1; _Trans. Linn. Soc. Bot._,

Ser. II. vol. 2). Sir Martin Conway in the Bolivian Andes found geese,

ducks, gulls, snipe, &c., numerous in suitable places up to 17,000 feet

(_Journ. Roy. Geogr. Soc._, 1899); whilst geese and teal were noticed by

Sir Joseph Hooker and others at elevations of 17,000 feet in the

mountains of Tibet (Hooker’s _Himalayan Journals_; _Journ. Linn. Soc.

Bot._, vol. 35, p. 147). These are all birds, as shown in Chapter

XXXIII., that are likely to disperse plants, and probably none more

effectually than the goose, of which Hawaii possesses a particular

variety or species. It may be remarked that geese, ducks, gulls, and

other birds use Cotula plumosa in Kerguelen for making their nests (Dr.

Kidder quoted by Mr. Dixon in his book on Birds’ Nests).

Sea-birds were probably the principal agents in carrying the achenes of

the early genera of the Compositæ to Hawaii. Dr. Hillebrand attached

importance to the tropic-bird (Phaethon) in the distribution of species

(Introd., p. 30); and since these birds breed at the crater of Kilauea

in Hawaii, 4,000 feet above the sea, and also high up in Tahiti

(Moseley), its agency is not unlikely, I am inclined to think, however,

that birds like the petrels and puffins, that in nesting burrow in the

ground, choosing places where the vegetation is thickest, and where they

would be likely to get seeds on their feathers, would be more efficient

agents. This is the view expressed by Prof. Moseley in Wallace’s _Island

Life_, p. 250. He considered that albatrosses, petrels, and puffins have

played a great part in the distribution of plants, and to some degree

especially account for the otherwise difficult fact that widely distant

islands in tropical seas have similar mountain plants. Birds, he says,

that in high latitudes, as at Tristan da Cunha and Kerguelen, often

burrow near the sea-level, in the tropics choose the mountains for their

nesting-place; and he refers to a puffin that nests on the top of one of

the high mountains of Viti Levu at an altitude of 4,000 feet, to a

petrel nesting among ferns at Tahiti at an elevation of 4,400 feet, and

to another petrel breeding in like manner in the high mountains of

Jamaica at a height of several thousand feet above the sea. He gives

point to these interesting remarks, which might be supplemented by data

from other parts of the world, by observing that it is not necessary

that the same species should now cover the range of the plants

concerned. The ancestor of the species might have carried the seeds, and

the range of the genus is alone sufficient. It may be added that, as I

have shown in Chapter XXXIII., sea-birds have been far more active

agents in the distribution of plants than many people might imagine. The

more recent observations of Ekstam in Spitzbergen have thrown

considerable light on this subject.

Having in the first place formed the opinion that the achenes of the

early Hawaiian Compositæ are suited for dispersal by birds, and then

shown that sea-birds were probably the principal agents, we are met with

the curious difficulty that in the case of the early Hawaiian genera of

Compositæ the complete suspension for ages of the means of dispersal is

involved in the circumstances that these genera are confined to the

Hawaiian group. We can attribute to the agency of existing sea-birds the

occurrence of the genus Lagenophora in the uplands of Hawaii, on the

mountain-tops of Fiji, and in Australia and New Zealand; but the agency

of birds as at present in operation does not assist us except indirectly

in the case of the genera restricted to Hawaii or to Tahiti. Is it

possible, we may inquire, to penetrate this mystery? Why, we may ask

with Mr. Hemsley, has the agency ceased acting, and why have its

operations been confined to the conveyance of seeds _to_ the islands and

not _from_ the islands as well (_Intr. Bot. Chall. Exped._, p. 66)? I

need scarcely add that the same question presents itself with all the

other peculiar genera of these islands, and in fact with endemic genera

all over the world. What can be stranger, it may be remarked, than the

limited distribution of the Pandanaceous genus Sararanga in the Western

Pacific, although suited for dispersal by frugivorous birds. This is

not, indeed, a special difficulty connected with oceanic islands; it

applies to the whole plant-world; yet it is possible that, as it is

exhibited by the Compositæ in these islands, we may be in a better

position to grapple with the problem. But before doing so it will be

requisite to look a little closer at these early Hawaiian genera of the

Compositæ.

The distribution within the archipelago of the genera and species of the

early Compositæ of Hawaii is worthy of notice from the light it throws,

not only on the relative antiquity of the genera, but also on the

subsequent conditions of isolation. Of the nine genera here referred to

five are distributed over most of the islands of the group. These

include all the genera possessing a number of species, namely,

Tetramolopium with seven species, Lipochæta with eleven, Campylotheca

with twelve, Dubautia with six, and Raillardia with twelve species. Of

the four genera remaining all have only two species, and are restricted

to two or three islands, Remya and Wilkesia being in both cases found in

Kauai and Maui, whilst Argyroxiphium is confined to the adjacent islands

of Maui and Hawaii, and Hesperomannia to those of Oahu, Lanai, and Maui.

These four genera that are restricted to only two or three islands are

the same before referred to as regarded by Hillebrand as the oldest,

partly on account of their isolated generic position, and partly because

in each case they only possess two species.

Although the early Hawaiian Compositæ were evidently originally

transported to most of the islands of the group, it is noteworthy that

their subsequent isolation from the rest of the world has in the later

ages been repeated within the limits of the archipelago. Of the 56

species, all of which are now endemic, 28, or just half, as shown in the

table on the following page, are confined to a single island. Of the

remainder, almost all are restricted to two or three adjacent islands.

Hillebrand gives only a solitary species, Lipochæta connata, as

occurring in all the islands. This suspension, to a great extent, of the

means of dispersal between the islands is also strikingly illustrated by

the Lobeliaceæ.

We have only to mention the flora of Fiji and those of the adjacent

groups of Samoa and Tonga to exclude them from any share in the early

era of the Compositæ in the Pacific. The prevailing adventitious

character of the Fijian Compositæ is indicated in the fact that the

species of the majority of the genera are included by Seemann in his

list of Fijian weeds. There are only one or two Fijian Compositæ, such

as the mountain species of Lagenophora and the littoral species of

Wedelia, that merit the special attention of the student of dispersal.

So also with Samoa, Reinecke enumerates eight species, of which six are

weeds either of aboriginal or of European introduction, the others being

the littoral Wedelia above alluded to, and a species of Blumea found

also in Fiji.

DISTRIBUTION OF THE ENDEMIC GENERA OF COMPOSITÆ IN THE HAWAIIAN ISLANDS.

+--------------+-----------------------------------------------------+-------+

| | Distribution of the Species. | |

| +---------+----------+----------+----------+----------+ |

+--------------+---------+----------+----------+----------+----------+-------+

|Remya | 2 | — | — | — | — | 2 |

|Tetramolopium | 1 | 4 | 2 | — | — | 7 |

|Lipochæta | 3 | 4 | 3 | — | 1 | 11 |

|Campylotheca | 5 | 4 | 3 | — | — | 12 |

|Argyroxiphium | 1 | 1 | — | — | — | 2 |

|Wilkesia | 2 | — | — | — | — | 2 |

|Dubautia | 4 | — | 2 | — | — | 6 |

|Raillardia | 9 | 1 | — | 2 | — | 12 |

|Hesperomannia | 1 | 1 | — | — | — | 2 |

+--------------+---------+----------+----------+----------+----------+-------+

| | 28 | 15 | 10 | 2 | 1 | 56 |

+--------------+---------+----------+----------+----------+----------+-------+

We have now, I venture to think, gone far to establish the existence of

an early “Composite” flora with mainly American affinities in the

Pacific islands, an ancient flora of which only the remnants now occur

in the uplands of Hawaii, Tahiti, and Rarotonga. That the achenes were

originally transported in birds’ plumage is, as we have seen, probable;

but we are still quite in the dark as to the causes of the subsequent

suspension of the means of dispersal and of the resulting period of

isolation, during which the original immigrant plants acquired their

endemic characters. In our uncertainty, therefore, we will look to Fiji

in the hope that in the absence of the early Compositæ from that group

we may find a clue that will enable us to divest this problem of some of

its difficulties.

It might be at first considered that since these peculiar genera of

Compositæ occur in the higher levels of Hawaii and Tahiti their absence

from Fiji might be connected with the relatively low altitude of those

islands, a character that is concerned with the exclusion from the

Fijian flora of many Hawaiian and Tahitian mountain plants (see Chapters

XXIII. and XXIV.). But this view is at once negatived by the fact that

Fitchia thrives in Rarotonga, an island which does not far exceed 2,000

feet in elevation. It is negatived also by the extensive development of

shrubby and arborescent Compositæ in the Galapagos Islands, on the

equator, in St. Helena in 16° South latitude, and in other tropical

islands, which are less than, or do not exceed, the Fijian Islands in

their altitude.

During the age of the Compositæ it is reasonable to suppose that the

dispersal was general over the Pacific. The absence of genera indicating

this era from the islands of the Fijian region, that is, from Fiji,

Tonga, and Samoa, would become intelligible if these groups were

submerged during this age of the general dispersal of the order over

this ocean. In my volume on the geology of Vanua Levu in Fiji, I have

shown that these island-groups of the Western Pacific emerged from the

sea towards the close of the Tertiary period, a conclusion that would

enable us to assign the age of the general dispersal of the Compositæ

over the tropical Pacific to an earlier portion of the same period.

In order, however, to make further progress in the discussion of this

difficult problem we are obliged to approach it from the outside. We

must in fact regard these genera from the standpoint of their position

as members of the vast and ancient order of the Compositæ. It is now

more than thirty years since Mr. Bentham completed his remarkable memoir

on the classification, history, and geographical distribution of the

Compositæ (_Journal Linnean Society, Botany_, London, Vol. 13, 1873).

Like De Candolle, when dealing with the facts of distribution, he

handled thousands of species, and as a result he drew certain inferences

which are of prime importance to students of plant-dispersal. In his

time the order included nearly 10,000 known species, and although this

number has since no doubt been considerably increased, it is not likely

that his main conclusions, in so far as they are free from purely

hypothetical considerations, will be materially affected by the later

discoveries.

Accepting the antiquity of the order, and regarding it as probably

dating far back in geological time, he observes that the evidence points

to a very wide dispersion of its original stock at an early period.

Africa, West America, and possibly Australia, possessed the order at the

earliest recognisable stage. There must have existed, he contends, at

this early period some means of reciprocal interchange of races between

these regions. Then followed a stoppage of communication, or a

suspension of the means of dispersal, between the tropical regions of

the Old and New Worlds; but long after communication was broken off in

the warmer regions, it still existed, as he holds, between the alpine

heights in those regions and also between the high northern latitudes of

both hemispheres. Referring particularly to the Hawaiian Group, he

considers that the large endemic element among the Compositæ indicates

that the ancient connection, whether with America or with Australasia,

has been so long severed as not to have left a single unmodified common

form. Fitchia, the Tahitian genus, as we have already remarked, is

regarded as the only remnant of an ancient Composite flora in the

tropical islands of the South Pacific.

In the light of these reflections it will be interesting to glance at

the general distribution of the shrubby and arborescent or woody

Compositæ. Mr. Hemsley, having generally discussed the subject, arrived

at the conclusion that, “although they form so large a proportion of the

floras of St. Helena, Juan Fernandez, the Sandwich Islands, and some

other islands, they are not specially insular.” There are scores of

them, he goes on to say, in South America, Africa, Madagascar, India,

Australia, and New Zealand from twenty to forty feet high, and more

truly arboreous than the insular ones; whilst nearly every sub-order has

its arboreous representatives. He was, however, unable to form any

definite opinion of the method of distribution of the woody Compositæ.

Taking those of St. Helena and Juan Fernandez, he observes that they are

not more closely allied to the Compositæ of the nearest continents than

they are to those of more distant regions. The occurrence of arboreous

Compositæ, belonging in each case to different tribes, in so many remote

oceanic islands, coupled with the distribution of the genera to which

they bear the greatest affinity, seems, he observes, to indicate that

they are the remains of very ancient types (_Introd. Bot. Chall.

Exped._, pp. 19-24, 66, 68; also Parts ii. p. 61, and iii. p. 23).

The further discussion of this subject would lead us into a wide field

of inquiry, quite beyond the scope of this work. There is, however, an

inference that I think we may legitimately draw from geological evidence

in this region. With respect to the antiquity of the woody Compositæ of

the Pacific as illustrated by the endemic genera, both Mr. Bentham and

Mr. Hemsley view them as belonging to ancient types. Mr. Wallace, in his

_Island Life_, a book that becomes more and more indispensable for the

student of dispersal as years progress, dwells on the importance of

these ancient Compositæ in the floral history of the Pacific islands. We

may look upon the Hawaiian Compositæ, he remarks, as representing the

most ancient portion of the existing flora, carrying us back to a very

remote period when the facilities for communication with America were

greater than they are now. The date of this period of oceanic dispersal

of the Compositæ we can now approximately determine, since these plants

are absent from the Fijian region, an area of submergence during the

Tertiary era. Before the island-groups of the Fijian region had emerged

towards the close of the Tertiary period the achenes of the early

Compositæ had been dispersed far and wide over the tropical Pacific.

But this is not all that we can infer from the convergence of these

independent lines of botanical and geological investigation. Mr. Bentham

observes that the tribes of the Compositæ had acquired the essential

characters now employed in classification before the dispersion of the

order over the Pacific. Since this general dispersion took place, as we

hold, during the Tertiary submergence of the island-groups of West

Polynesia (Fiji, Tonga, Samoa), it follows that the birth of the tribes

of the Compositæ antedates that period. If this interesting order could

supply us with a “datum-mark” in the history of the Pacific floras, it

would be stated in terms of the development of specific and generic

characters, but not of those of a tribe.

_Summary of Chapter._

(1) The Hawaiian Islands present the same contrast with the Fijian and

Tahitian groups as regards the development of new species in the case of

the flowering plants that they offer in the case of the vascular

cryptogams (ferns and lycopods). But the contrast is intensified, and it

is further emphasised as respecting the flowering plants by the

evolution of a large number of endemic genera.

(2) This great preponderance of peculiar species and genera in Hawaii is

not to be connected with the relative antiquity of the group but with

its degree of isolation.

(3) The earliest stage of the flowering plants of the islands of Hawaii

and of Eastern Polynesia (the Tahitian region) is indicated by the

endemic genera, particularly those of the Compositæ and Lobeliaceæ. Such

genera are numerous in Hawaii, and occur also in the Tahitian region, as

in Tahiti and Rarotonga; but do not exist in the groups of the Fijian

region (Fiji, Tonga, and Samoa).

(4) The endemic genera of the Hawaiian Compositæ are mainly American in

their affinities. The relationship of the solitary Tahitian genus

(Fitchia) is still a subject of discussion.

(5) In the Hawaiian Islands, as well as in Tahiti and Rarotonga, the

plants of the endemic genera of Compositæ are, as a rule, arborescent or

shrubby; and in the first two localities they are mainly restricted to

the higher levels.

(6) In discussing the mode of dispersal of the achenes of the original

genera we have also to explain why the process of dispersal has been in

the main suspended.

(7) It is shown that the achenes of these early Compositæ were in all

probability suited for dispersal in birds’ plumage.

(8) Yet the isolating influence that cut off these genera from the

outside world has, in later ages, been active within the limits of the

Hawaiian archipelago, with the result that half the species are not

found in more than a single island. Inter-island dispersal has,

therefore, been also largely suspended.

(9) The absence of endemic genera of Compositæ from Fiji, Tonga, and

Samoa cannot be attributed to unsuitable climatic conditions connected

with the relatively low elevation of those islands as contrasted with

those of Hawaii, since a species of Fitchia abounds in Rarotonga, which

is not far over 2,000 feet in elevation. Shrubby and arborescent

Compositæ of peculiar types also occur in the Galapagos and other

tropical islands not more elevated than the Fijis.

(10) These endemic genera are the remains of an ancient Composite flora

in the islands of the tropical Pacific, and ages have elapsed since the

severance of their connections with regions outside.

(11) According to Mr. Bentham the Compositæ were distributed over

Africa, West America, and possibly Australia, at an early period, but

subsequent to the differentiation of the tribes of the order. Some means

of reciprocal interchange of races between these regions then existed.

Then followed a suspension of the means of dispersal between the

tropical regions of the Old and New Worlds except between the alpine

heights of those latitudes.

(12) It is inferred by the author of this volume that the general

dispersion of the early Compositæ over the Pacific took place during the

Tertiary submergence of the island-groups of the Fijian region (Fiji,

Tonga, and Samoa), and that their absence from that region may be thus

explained. At the time of this general dispersion, as above pointed out,

the tribes of the Compositæ had been already differentiated.

CHAPTER XXII

THE ERA OF THE ENDEMIC GENERA (_continued_)

THE COMPOSITÆ AND LOBELIACEÆ (_continued_)

THE AGE OF THE TREE-LOBELIAS

The distribution of the arborescent Lobeliaceæ.—On the upper flanks of

Ruwenzori.—The Lobeliaceæ of the Hawaiian Islands.—The Lobeliaceæ of

the Tahitian or East Polynesian region.—The capacities for

dispersal.—The explanation of the absence of the early Lobeliaceæ from

West Polynesia.—The other Hawaiian endemic genera.—The Fijian endemic

genera.—Summary.

THE Lobeliaceæ rank with the Compositæ in the prominence of their

position in the early Pacific floras. Though absent, as far as is known,

from Fiji, they are represented in Hawaii by 58 species, all endemic and

belonging to six genera, of which five are not found elsewhere. All

possess, as Hillebrand remarks, a woody stem, by far the greater number

being either tall shrubs, 5 or 6 feet high, or small trees, 10 to 20

feet or more in height. In the East Polynesian or Tahitian region, the

order is represented by two genera containing in all five known species

and restricted to those islands. One genus is common to the islands of

Tahiti and Rarotonga, and the other is confined to Raiatea. The species

may be shrubby or arborescent.

It was for some time considered that the oceanic archipelagoes of the

Pacific were the exclusive centres of these singular arborescent

Lobeliaceæ (I am here quoting Baillon in his _Natural History of

Plants_). And indeed this idea would receive some support from the

circumstance that Dr. Hillebrand, in his work on Hawaii, says little or

nothing about the affinities or general relations of plants which he

enthusiastically termed “the pride of our flora.” His death in 1886

deprived his work of its crowning piece, a discussion of “the

interesting questions of the origin and development of the Hawaiian

flora” (see the Editor’s Introduction, p. ix.). In no group of plants is

this want more keenly felt than with the Lobeliaceæ. Yet in his time the

explorations had yet to be made that could set the student of

plant-distribution on the road to investigate this problem.

It was true, no doubt, that types analogous to those of the Hawaiian

Lobeliaceæ were known from the American and African continents. Thus

Oliver in his _Flora of Tropical Africa_, published in 1877, gives an

account of the species of Lobelia then known from the mountains of this

region. The genus was, however, not entirely confined to mountainous

districts, but it would almost seem that most of the high mountains of

Equatorial Africa had their peculiar species, some of them being

tree-like and others shrubby. Two mountain species were recorded from

Abyssinia, one of them from an elevation of 11,000 to 13,000 feet and

growing to a height of 12 to 15 feet, the other from an altitude of

about 8,000 feet; another, Lobelia Deckenii, attaining a height of 4

feet, was recorded from the uplands of Kilimanjaro, 12,000 to 13,000

feet above the sea, and yet another from the mountains of Fernando Po,

at an altitude of 9,000 feet. So again, in the case of the American

continent, Hemsley, writing in 1885 (_Intr. Bot. Chall. Exped._, p. 32),

speaks of arborescent species of the American genera Centropogon,

Siphocampylus, &c.; and Baillon in his _Natural History of Plants_

(Engl. edit. viii. 350) refers to the similar Tupas and Haynaldias from

South America. But what the student of plant-distribution looked for was

not merely the occurrence of “tree-lobelias” in other parts of the

world, but also the reproduction of these wonderful plants under the

same conditions and on the same scale as those familiar to him on the

Hawaiian mountains. He has accordingly had to wait for the results of

the more recent explorations of the mountains of Central Africa in order

to obtain his wish.

On the upper flanks of Ruwenzori, Kilimanjaro, and Kenya, at elevations

of 9,000 to 13,000 feet and reaching to the snow-line, there flourish in

boggy portions of the forest arborescent Lobeliaceæ that attain a height

of 15 or 20 feet. They have the habit sometimes of a Dracæna and

sometimes of an Aloe, and do not exhibit the branching trunks so

characteristic of the Hawaiian genus of Clermontia. They all belong,

however, to the genus Lobelia, and thus do not display the extensive

differentiation of the endemic genera of Hawaii. Nor, apparently, has

there been the same degree of formative energy in the development of

species, since only about half a dozen species are hitherto known. We

find, however, produced on these lofty mountains of Equatorial Africa

the same climatic conditions under which the arborescent Lobeliaceæ

flourish in Hawaii, namely, the very humid atmosphere, the heavy

rainfall, and the mild temperature; and if there are important contrasts

in their character and in the amount of differentiation which they have

undergone in the two regions, the one a continental and the other an

insular region, it will be from such contrasts that some of the most

interesting results of this comparison of a mountain of Central Africa

with an island of the open Pacific will be ultimately derived (see Sir

H. Johnston’s _Uganda Protectorate_, 1902, and _Kilimanjaro Expedition_,

1886; also _Trans. Linn. Soc. Bot._, ser. 2, vol. 2, p. 341.)

THE LOBELIACEÆ OF THE HAWAIIAN AND OF THE EAST POLYNESIAN OR TAHITIAN

ISLANDS.[1]

HAWAIIAN ISLANDS.

+-----------+-----+-------------+-------------+--------------------------------------+

| | c | | | +-------------+-----------+

| | o i | | | | | |

| | f e | | | | | |

| | s | | | | | |

| | . | | | | | |

+-----------+-----+-------------+-------------+------------+-------------+-----------+

| | | | | | | |

|Lobelia | 5 | Non-endemic.| General. | 4 to 6 | 2,000 to | Bridges, |

| | | | | | | |

| | | | | | | |

| | | | | 10 to | 4,000 feet | |

| | | | | | | |

|Delissea | 7 | Endemic. | General. | 5 | 1,000 to | Woods and |

| | | | | | | |

+-----------+-----+-------------+-------------+------------+-------------+-----------+

EAST POLYNESIAN OR TAHITIAN ISLANDS.

+-----------+-----+-------------+-------------+------------+-------------+-----------+

|Sclerotheca| 4 | Endemic in |{Tahiti, | 6 to 25 | 1,500 to | Humid |

| | | E.Polynesia.|{Rarotonga. | feet. | 3,000 feet. | wooded |

| | | | | | | |

+-----------+-----+-------------+-------------+------------+-------------+-----------+

Footnote 1:

The materials are nearly all derived from the works of Hillebrand and

Drake del Castillo. Some of those relating to the elevations in Hawaii

are supplemented from my notes. All the genera are endemic except

Lobelia, of which all the species are apparently endemic, excepting

perhaps one, which, according to Hillebrand, resembles greatly a

species from the Liukiu Islands.

Footnote 2:

The range of the heights of different species of Clermontia is from 5

or 6 feet for shrubs to 25 feet for trees.

Footnote 3:

The heights attained by different species of Cyanea range from 3 or 4

feet to between 30 and 40 feet, thus:—

In 8 species 3 to 6 feet.

In 9 species 6 to 10 feet.

In 7 species 10 to 15 feet.

In 3 species 15 to 25 feet.

In 1 species 30 to 40 feet.

THE LOBELIACEÆ OF THE HAWAIIAN ISLANDS.

Having thus prepared the way, I will proceed to the discussion of the

Hawaiian Lobeliaceæ, dealing first with their “station.” Their vertical

distribution is well illustrated in the large and lofty island of

Hawaii. Whilst the woody Compositæ, as before described, are most at

home on the open-wooded and often scantily-forested slopes between 5,000

and 9,000 feet, the Lobeliaceæ are most characteristic of the middle or

true forest zone that extends from 2,000 or 3,000 feet to between 5,000

and 6,000 feet above the sea. This lies within the region of clouds and

mists, and it is here that the rain-belt or area of greatest rainfall is

situated, the annual amount averaging probably 150 to 200 inches. It is

in such humid conditions that, as Hillebrand observes, trees and jungle

are developed in greatest luxuriance; and it is here that “the

Lobeliaceæ exhibit their most striking forms.” The traveller, as he

ascends the mountains, finds the Tree-Lobelias in the region of mist and

rain-cloud; and he is lucky if he escapes the usual downpour and

encounters only a fine drizzling rain.

The mild climate of this region is indicated by a mean annual

temperature ranging probably with elevation from 65° to 55° F. It is

secure from the frosts of the upper slopes of the mountain; whilst at

the same time it is above the regions of tropical heat. There is,

however, no doubt that when the forests extended to the coasts, as they

occasionally do now on the north side of Hawaii, the Lobeliaceæ occurred

much lower down than they do at present, though still only attaining

their greatest development in size and number in the higher levels.

Thus, at rare intervals, I noticed in the forests of Hamakua and Kohala,

where they descended to the coasts, species of Clermontia at an

elevation of only 500 or 600 feet above the sea.

Probably in no part of the Hawaiian Islands are the conditions under

which the “Tree-Lobelias” thrive better illustrated than on the higher

slopes of Mount Eeka, a bulky mountain mass about 6,000 feet in height,

forming the western portion of Maui. Its flat top, as Hillebrand

observes, is wrapped in a cloud of mist nearly the whole year. On the

boggy surface of the summit, where Acæna exigua gives a tussocky

appearance, and Sphagnum or bog-moss abounds, flourish Cyperaceæ,

Lycopods, and Selaginellæ; and here Drosera longifolia and a peculiar

species of marsh violet (Viola mauiensis) find a home. The upper slopes,

down to 4,000 feet, present similar moist conditions, and here in an

open-wooded district, associated with Cyrtandræ, Marattias, and true

Tree-Ferns, the ground being covered with Lycopods, the “Tree-Lobelias”

abound. I noted four kinds within two hundred yards. Of the humidity of

the upper slopes of Mount Eeka I have a very vivid recollection, and my

experience of passing a night on that mountain is described in Chapter

XIX.

The Lobeliaceæ, as Hillebrand remarks, occur invariably as isolated

individuals. I was often struck, however, with the preference the genera

showed for particular localities. Thus, Clermontia is well represented

on the western slopes of Mount Eeka, Delissea on the northern slopes of

Hualalai (3,800 to 4,500 feet), Cyanea on the Hamakua slopes of Mauna

Kea (2,300 to 4,100), and Lobelia on the southern slopes of Mauna Loa

behind Punaluu (2,000 to 3,500 feet).

To the student of geographical distribution the Hawaiian Lobeliaceæ are

of especial interest. Mr. Hemsley observes that they have their greatest

affinities in America (_Intr. Bot. Chall. Exped._, p. 68). M. Drake del

Castillo, in his “Mémoire couronné par l’Académie des Sciences” (Paris,

1890), remarks that these plants connect Hawaii with America just as the

Goodeniaceæ link the same group with Australia. This is what we might

have expected since the centre of the order is in America, principally

in the Mexican and Andine regions (Drake del Castillo, _Flore Polyn.

Franc._, xi.).

Though five out of the six genera are endemic, the sixth, that of

Lobelia, has a world-wide distribution. Here then, we have a genus that

belongs strictly to the next or second stage of the plant-stocking of

the Hawaiian Group, namely, when the non-endemic genera now containing

endemic species were introduced. As with the Composite genera,

Campylotheca and Lipochæta, Lobelia marks the beginning of the new or

the close of the old era. It is, however, necessary to point out that

many of the conditions favouring luxuriant and rank vegetable growth are

pre-eminently represented in the zone of the Lobeliaceæ. In these

soft-stemmed plants with their copious milky sap and large fleshy

flowers, sometimes two or three inches long, the very redundancy of

growth would tend both to exaggerate and to disguise the generic

distinctions. To the ordinary observer these “Tree-Lobelias” call up

vague notions of a flora of a bygone age, and by their _bizarre_

appearance he might with some excuse be led to give play to his

imagination when describing them; but the systematic botanist, seeing

through their disguise, frames rather more prosaic notions of their

antiquity and degree of differentiation. According to my view, the first

Hawaiian Lobeliaceæ occupied open, exposed localities such as are held

by the decadent genus Brighamia now, and acquired their monstrous form

in the humid forests of a later age. (See Perkins in Note 80.)

In his monograph on the Campanulaceæ (Engler’s _Nat. Pflanz. Fam._, teil

4, abth. 5, 1894), S. Schönland, speaking of the sub-family Lobelioideæ,

places the seven endemic Hawaiian and Tahitian genera in a group by

themselves. Though, as he observes, the Hawaiian tree-forms appear at

first sight to constitute a natural group, they cannot be sharply

distinguished from other forms, and even in habit come near some Indian

and Abyssinian types of Lobelia. In their treatment, he says, they

should all go together, and he does not approve of the endeavours of

some botanists to isolate one of them (Brighamia) from the rest and to

connect it with the Australian genus Isotoma.

It is also to be noted that whilst four of the Hawaiian genera are more

or less dispersed over the group, one (Brighamia) with only one species

is confined to the islands of Molokai and Niihau, the double habitat

being suggestive of its approaching extinction. Another (Rollandia) with

six species is restricted to the island Oahu. Cyanea, which possesses

twenty-eight out of the total of fifty-eight species, may, from the

point of view of its formative energy, be regarded as in its prime. It

is thus apparent that, as with the Compositæ, the early Lobeliaceous

immigrants were not all contemporaneous arrivals.

DISTRIBUTION OF THE LOBELIACEÆ IN THE HAWAIIAN ISLANDS.[4]

Column headings:

A: Brighamia.

B: Lobelia.

C: Clermontia.

D: Rollandia.

E: Delissea.

F: Cyanea.

G: Total.

+----------------------------------+----+----+----+----+----+----+----+

| Hawaiian Lobeliaceæ. | A | B | C | D | E | F | G |

+----------------------------------+----+----+----+----+----+----+----+

| Species confined to one island | — | — | 6 | 6 | 4 | 22 | 38 |

| Species confined to two islands | 1 | 2 | 2 | — | 2 | 5 | 12 |

| Species confined to three islands| — | 1 | 2 | — | 1 | 1 | 5 |

| but still endemic | — | 2 | 1 | — | — | — | 3 |

| +----+----+----+----+----+----+----+

| | 1 | 5 | 11 | 6 | 7 | 28 | 58 |

+----------------------------------+----+----+----+----+----+----+----+

Footnote 4:

All the species are endemic.

Another interesting fact of distribution, brought out by an analysis of

Hillebrand’s materials and illustrated in the subjoined table, is that

out of the fifty-eight Hawaiian species, all of which are endemic,

thirty-eight, or 66 per cent., are recorded from only one island. In

most of the other cases they are recorded from two or three islands,

usually adjacent, like Maui and Molokai; and except in the instance of

two species of Lobelia and one species of Clermontia they never range

over the length of the group.

These facts speak eloquently of the suspension to a great extent of the

agencies of dispersal in recent times within the group. Some corrections

of the figures will be rendered necessary by future investigations, but

the main conclusion will not be materially affected. Such facts are

paralleled in the distribution of the Hawaiian insects, mollusca, &c.;

but these matters need only be mentioned here. We might, indeed, have

expected, apart from other considerations, that the isolation of the

Hawaiian Lobeliaceæ from their kindred in other parts of the world would

not have been reproduced within the group itself. This, however, is not

the case; and we now see that not only have they been deprived for ages

of their means of distribution over the Pacific, but that even within

the archipelago their transportal from island to island has been largely

suspended. We have before arrived at similar conclusions with regard to

the early Compositæ, when we saw that about half the species were not

found in more than one island. It is therefore evident that the same

great principle regulating the operations of the distributing agencies

has influenced to a similar extent both the Compositæ and the Lobeliaceæ

of the Hawaiian Group.

THE LOBELIACEÆ OF THE TAHITIAN OR EAST POLYNESIAN REGION.

The order is represented in this region by two endemic genera,

Sclerotheca of Tahiti and Rarotonga, and Apetahia of Raiatea. These

islands are, however, not sufficiently large for the extensive

development of the arborescent Lobeliaceæ, such as we find in Hawaii.

The species in both genera are either arborescent or shrubby; but I do

not gather that they give any character to the floras of these islands.

According to the data given by Drake del Castillo for one of the two

peculiar species of Sclerotheca occurring in Tahiti, these plants grow

on the humid wooded slopes of the mountains at elevations of 2,000 to

3,000 feet. Whilst in one species the plants attain a height of 10 to 25

feet, in the other they do not exceed 10 feet. Rarotonga possesses a

peculiar species of Sclerotheca, 4 to 6 feet high, which was discovered

by Cheeseman growing plentifully on the upper slopes of the highest

mountain of the island at altitudes of 1,500 to 2,200 feet. The same

botanist also came upon a second species of the genus on another

mountain in Rarotonga at elevations of 1,000 to 1,500 feet, but it was

rare and has not yet been described. The other genus, Apetahia, has only

been recorded from Raiatea, where it is represented by a solitary

species (6 feet high) growing, according to Nadeaud, in the mountains of

that island.

It is apparent that the dispersal of these genera of the Lobeliaceæ

amongst the groups of Eastern Polynesia ceased long ago. From the

circumstance that Sclerotheca exists in Tahiti and in Rarotonga, which

are about 650 miles apart, it may be inferred either that the genus was

introduced into this region from outside, or else, which is perhaps more

probable, that it was developed in Tahiti whence it was transported to

Rarotonga. Hemsley speaks of this Tahitian genus as seemingly marking a

former wide extension of the Hawaiian arborescent type of the Lobeliaceæ

(_Introd. Bot. Chall. Exped._, p. 68). This is the view that will be

adopted in this chapter, and it is precisely the view advocated by

Bentham and followed here, in the case of the early Compositæ of the

Pacific.

Observations of a Naturalist in the Pacific Between 1896 and 1899, Volume 2 Plant-Dispersal · 第 38 / 47 章

Now, what are these changes? How has the bird acted unconsciously such a