Transcriber’s Note

The cover image was created by the transcriber and is placed in the public domain.

Some corrections have been made to the printed text. These are listed in a second transcriber’s note at the end of the text.

OBSERVATIONS OF A NATURALIST IN THE
PACIFIC BETWEEN 1896 AND 1899

[Frontispiece.

Selala (Vanua Levu, Fiji) (1⁄3).

Fruits with seedlings nearly ready to fall from the tree of Rhizophora mangle (shortest) and Rhizophora mucronata (longest). From Vanua Levu, Fiji. (1⁄4 of the true length.)

Rhizophora mangle (Vanua Levu, Fiji) (1⁄4).

Rhizophora mucronata (Vanua Levu, Fiji) (1⁄5).

OBSERVATIONS OF

A NATURALIST IN

THE PACIFIC BETWEEN

1896 AND 1899

BY

H. B. GUPPY, M.B., F.R.S.E.

VOLUME II

PLANT-DISPERSAL

London

MACMILLAN AND CO., Limited

NEW YORK: THE MACMILLAN COMPANY

1906

All rights reserved

Richard Clay and Sons, Limited,

BREAD STREET HILL, E.C., AND

BUNGAY, SUFFOLK.

Dedication

TO THOSE NUMEROUS PERSONS TO WHOM I WAS INDEBTED FOR

GREAT KINDNESS AND ASSISTANCE DURING MY

SOJOURN IN HAWAII AND FIJI

PREFACE

Although this volume contains a great amount of original material, I am largely indebted to the labours of my predecessors for its present form; and a scheme that at first was limited only to my own observations in the Pacific has gradually extended itself to the general subject of plant-dispersal. The farther I proceeded in my work the more I realised that the floras of the Pacific islands are of most interest in their connections, and that the problems affecting them are problems concerning the whole plant-world. Deprived of the writings of Seemann, Hillebrand, Drake del Castillo, and other botanists, several of whom have lived and died in the midst of their studies of these floras, and without the aid of the works of Hemsley and Schimper, generalisers who have mainly cleared the way for the systematic study of plant-distribution and plant-dispersal, it would not have been possible for me to accomplish such an undertaking.

My interest in plant-dispersal dates back to 1884, when, whilst surgeon of H.M.S. Lark, in the Solomon Islands, I made some observations on the stocking of a coral island with its plants, which were published in the Report on the Botany of the “Challenger” Expedition. In 1888 I followed up the same line of investigation during a sojourn of three months on Keeling Atoll, and during a journey along the coasts of West Java. But realising that as yet I had barely touched the fringe of a great subject, and that several years of study would be required before one could venture even to appreciate the nature of the problems involved and much less to weigh results, I took advantage of the circumstances of my life to make, between the years 1890 and 1896, a prolonged investigation of the plants of the British flora, mainly from the standpoint of dispersal by water. This involved the study of the seed-drift of ponds and rivers and of the plants supplying it, a study which brought me into close relation with aquatic and sub-aquatic plants. This line of investigation led me into contact with many other aspects of plant-life; and as time went on my field of interest extended to the plants of dry stations and to the bird as an agent in plant-dispersal. Only a few of these results have been published, as in the journals of the Linnean Society and of the Royal Physical Society of Edinburgh as well as in the pages of Science Gossip. They lie for the most part still within my note-books, and fitly so, since I regarded such studies chiefly as a preparation for the investigation of the general question of plant-dispersal.

When again, in October, 1896, I found myself once more in the Pacific, the subject was taken up again with zeal; but my larger experience had only increased my diffidence, and the unknown looked so overwhelming that I settled down for the next three years content with merely making experiments and recording observations. Here again the main problem was attacked through the study of seed-buoyancy, and gradually it led me to the systematic study of the mangroves and of the beach-plants, whilst my inland excursions brought me into familiarity with the plants of the interior. My geological exploration of the island of Vanua Levu, in Fiji, greatly assisted me by giving a method to my botanical examination of the island.

Whilst working out my geological collections in England, in the years 1900-1902, I devoted an hour or two daily to the elaboration of my botanical notes and to a consideration of the problems concerned. During a winter in Sicily I took up again the subject of the beach-plants; and after the publication of the volume on the geology of Vanua Levu I was able to accomplish a plan, for years in my dreams, of visiting the eastern shores of the Pacific. During a period of three months from December, 1903, to March, 1904, I examined the littoral flora of the west side of South America at various localities between Southern Chile and Ecuador; and finally completed this investigation by comparing the shore-plants on the Pacific and Atlantic coasts of the isthmus of Panama. Returning to England with a fresh collection of data, I passed many months in elaborating and arranging all my notes, waiting vainly for a clue to guide me in framing a scheme by which I could bring the results of many years of work into some connected form. At last I decided once again to take the floating seed as my clue, and without any prearranged plan I allowed the work to evolve itself. Now that it is finished, I can see some obvious defects; but if any other plan had been adopted I scarcely think that I should have been more successful in piecing together in a single argument materials resulting from so many years of research and relating to so many aspects of plant-life.

Yet the final object of a naturalist would be but a sorry one, if his aim were only to write a treatise and append his name to it. His personal faith lies behind all his work; and no one can pursue a long line of study of the world around him without rising from his task with some convictions gained and some convictions lost.

As far as the observation of Nature’s processes at present in operation can guide us, the world presents itself to us only as a differentiating world. We can perceive, it is true, a progressive arrangement of types of organisms from the lowest to the highest, and we can perceive a development of varieties of the several types; but the only process evident to our observation is that concerned with the production of varieties of the type. Nature does not enlighten us as to the mode of development of the type itself. We can, for instance, detect in actual operation the process by which the different kinds of bats or the different kinds of men have been developed; but there is no principle in Nature evident to our senses that is concerned with type-creation. Though we can supply it by hypothesis, we cannot discover it in fact. On the other hand, the evidence of differentiation is abundant on all sides of us, both in the organic and in the inorganic worlds. The history of the globe has ever proceeded from the uniform to the complex; and in the closing chapter of this book an endeavour is made to connect the differentiation of plant and bird with the differentiation of the conditions of existence on the earth. But this leaves no room for the development of new types of organisms; and so far as observation of the processes of Nature at present working around us can guide us, each type might well be regarded as eternal. We can never hope to arrive at an explanation of the progressive development of types by studying the differentiating process; and since the last is alone cognisable for us, evolution, as it is usually termed, becomes an article of our faith, and of faith only.

In illustration of this argument, let me take the case of the races of men. We see mankind in our own day illustrating the law of differentiation all over the globe, as far as physical characters are concerned. Just as the ornithologist would postulate a generalised type in tracing the origin of various allied groups of birds, so the anthropologist, guided by his observation of the changes now offered by man in different regions, would postulate a generalised original type as the parent-stock of mankind. Observation of the processes of change now in operation by no means leads us to infer that such a generalised type was an anthropoid ape, or even simian in character. In so doing we should be forming a conclusion not warranted by the observation of existing agencies of change, and we should be confusing the two distinct processes of evolution and differentiation, or rather of progressive and divergent evolution, of which the last alone comes within our field of cognition. The study of variation can do no more than enable us to ascertain the mode of development of different kinds, we will say, of birds or of men. The origin of the type lies outside our observation. “Given the type, to explain its origin”: this is the problem we can never solve, and Nature aids us nothing by the study of her ways. On the other hand, there is the subsidiary problem.... “Given a type, to explain its varieties” ...; and here Nature’s processes are apparent to us in a thousand different shapes.

It might seem that the presumptive evidence connecting man in his origin with the monkeys is so strong that, supposing his simian descent were regarded as a crime, a jury would without hesitation pronounce his guilt; but until some observer of the processes followed by Nature can bridge over the gap that divides man from the ape, until indeed he can offer a legitimate illustration of how it is accomplished in similar cases in our own day, the gap remains. Those who have read the recent work of Prof. Metchnikoff on the Nature of Man will properly regard his chapter on the simian origin of man as a brilliant argument advanced by a most competent authority. Yet he fails to complete his case by bridging over this gap, and can only appeal to the results of the now famous researches of De Vries concerning the mutations of the evening primrose (Œnothera). It is probable, he says, that man owes his origin to a similar phenomenon (English edition, p. 57). Several objections could be raised against this illustration from the plant-world, the most important of them lying in the circumstance that these mutations could only be urged as instances of the sudden development of new species of the evening primrose type. They merely illustrate the process of differentiation from a given type, and by no means represent the process of progressive evolution from a simian to a man.

However, look where we may—and this is the great lesson I have learned from my researches in the Pacific islands—Nature does not present to our observation any process in operation by which a new type of organism is produced. The processes involved lie hidden from our view. The channels by which impressions from the outside world reach us are comparatively few; and although it seems likely that the future development of man will be mainly concerned with the acquirement of additional sense-channels, no newly acquired sense will enable him to be at once an actor in and a spectator of the great drama presented in the organic world. That a creature should be able to get at the back of its own existence, or, in other words, to penetrate the secret of its own creation, is unthinkable. Outside the limited field of observation that immediately surrounds us extends the region where reason alone can guide us, and beyond lies the realm where reason fails and faith begins.

H. B. GUPPY.

November 8th, 1905.

LIST OF SOME OF THE PRINCIPAL AUTHORITIES QUOTED IN THIS VOLUME,
WITH AN ENUMERATION OF THE AUTHOR’S BOTANICAL PAPERS

Burkill, I. H., “The Flora of Vavau, one of the Tonga Islands,” Journal of the Linnean Society, vol. xxxv., Botany, 1901.

Cheeseman, T. F., “The Flora of Rarotonga,” Transactions of the Linnean Society, 2nd Ser., Botany, vol. vi., part 6, 1903.

Drake del Castillo, E., “Flore de la Polynésie Française,” Paris, 1893.

“Remarques sur la Flore de la Polynésie” (Mémoire couronné par l’Académie des Sciences), Paris, 1890.

Eggers, Baron H. von, “Die Manglares in Ecuador,” Botanisches Centralblatt, No. 41, 1892.

“Das Küstengebiet von Ecuador,” Deutsche Geographische Blätter, heft 4, band 17, Bremen, 1894.

Ekstam, O., “Einige blütenbiologische Beobachtungen auf Novaja Semlja,” Tromso Museums Aarshefter, 18, 1895.

“Einige blütenbiologische Beobachtungen auf Spitzbergen,” Tromso Museums Aarshefter, 20, 1897.

Guppy, H. B., “The Dispersal of Plants as illustrated by the Flora of Keeling Atoll,” Journal of the Victoria Institute, London, 1889.

“The Polynesians and their Plant-Names,” Journal of the Victoria Institute, London, 1896.

“The River Thames as an Agent in Plant-Dispersal,” Journal of the Linnean Society, Botany, vol. xxix., 1891-93.

“River-Temperature,” part iii., Proceedings of the Royal Physical Society of Edinburgh, 1896. (The first two parts deal principally with the temperature of ponds and rivers, whilst in the last part the thermal conditions are discussed especially in connection with the life of aquatic plants.)

“On the Postponement of the Germination of the Seeds of Aquatic Plants,” Proceedings of the Royal Physical Society of Edinburgh, 1897.

“On the Temperature of Springs as especially illustrated by the Wandle and other Tributaries of the Thames.” (This paper, of which I have no copy, was published in the Journal of the Royal Meteorological Society, about 1895. It throws light on the thermal conditions of plants in springs.)

“Water-Plants and their Ways,” Science Gossip, Sept., Oct., Nov., 1894. (The various modes of dispersal of land as well as water plants are here dealt with, their thermal conditions are discussed, and in the November number are given the results of four years’ observations on the life-history and life-conditions of Ceratophyllum demersum.)

“Caddis-Worms and Duckweed,” Science Gossip, March, 1895. (A short note.)

“Stations of Plants and Buoyancy of Seeds,” Science Gossip, April and May, 1895.

“Irregularity of some Cotyledons,” Science Gossip, September, 1895.

“Plants of the Black Pond, Oxshott,” Science Gossip, October, 1895.

“On the Habits of Lemna minor, L. gibba, and L. polyrrhiza,” Journal of the Linnean Society, Botany, vol. xxx. (This paper contains the results of three years’ systematic observations of these plants.)

“The Distribution of Aquatic Plants and Animals,” The Scottish Geographical Magazine, January, 1893.

Hemsley, W. B., “Report on the Botany of the Challenger Expedition,” 1885.

“The Flora of the Tonga Islands,” Journal of the Linnean Society, Botany, vol. xxx.

Hillebrand, W., “Flora of the Hawaiian Islands,” Heidelberg, 1888.

Horne, J., “A Year in Fiji,” London, 1881.

Kolpin Ravn, F., “Om Flydeevnen hos Froene af vore Vand-og Sumpplanter,” Botanisk Tidsskrift, 19 bind., 2 hefte, Kjobenhavn, 1894 (“On the Floating Capacity of the Seeds of Aquatic and Marsh Plants”). (A résumé in French is appended to the paper.)

Martins, Ch., “Expériences sur la Persistance de la Vitalité des Graines flottant à la Surface de la Mer,” Bull. Soc. Botanique de France tome iv., 1857.

Nadeaud, J., “Enumération des Plantes indigènes de l’Ile de Tahiti,” Paris, 1873.

Penzig, O., “Die Fortschritte der Flora des Krakatau,” Annales du Jardin Botanique de Buitenzorg, 2 ser., tome 3, Leide, 1902.

Perkins, R. C. L., “Fauna Hawaiiensis,” vol. i., part iv. (Vertebrata) Cambridge University Press, 1903.

Reinecke, F., “Die Flora der Samoa-Inseln,” Engler’s “Botanische Jahrbücher,” band xxv., heft v., Leipzig, 1898.

Schimper, A. F. W., “Die indo-malayische Strandflora,” Jena, 1891.

Seemann, B., “Flora Vitiensis,” London, 1865-73.

Sernander, R., “Den Scandinaviska Vegetationens Spridnings-biologi,” Upsala, 1901.

Thuret, G., “Expériences sur des Graines de diverses Espèces plongées dans de l’eau de Mer,” Archives des Sciences (Phys. et Nat.) de la Bibliothèque Universelle, tome 47, Geneva, 1873.

Treub, M., “Notice sur la nouvelle Flore de Krakatau,” Annales du Jardin Botanique de Buitenzorg, 1888.

Note.—Amongst the works quoted which are not specially particularised in the text are Scott Elliot’s “Nature Studies,” 1902, and Beal’s “Seed Dispersal,” Boston, 1900.

CONTENTS

PrefacePages [vii—x]
List of some of the Principal Authorities quoted, with an Enumeration of the Author’s Botanical Papers Pages [xiii—xv]
List of Illustrations Page [xxvii]
Additions and CorrectionsPage [xxviii]

CHAPTER I

INTRODUCTION

The study of insular floras.—Their investigation in this work from the standpoint of dispersal.—The significance of plant-distribution in the Pacific.—The problems connected with the mountain-flora of Hawaii.—The persistence of dispersing agencies at the coast, their partial suspension on the mountain-top, their more or less complete suspension in the forest, and the effect on the endemic character of plants.—The connection between the endemism of birds and plants.—The relative antiquity of plants of the coast, forest, and mountain-top.—The genetic relation between coast and inland species of the same genus.—The ethics of plant-dispersal.—Evolution takes no heed of modes of dispersal.—The seed-stage is the price of Adaptation.

Pages [1-11]

CHAPTER II

THE FLORAS OF THE PACIFIC ISLANDS FROM THE STANDPOINT OF DISPERSAL

BY CURRENTS

The initial experiment.—The proportion of littoral plants.—The two great principles of buoyancy.—The investigations of Professor Schimper.—The investigations of the author.—The great sorting process of the ages.—Preliminary results of the inquiry into the buoyancy of seeds and fruits.

Pages [12-22]

CHAPTER III

THE LESSON OF THE BRITISH FLORA

Results of observations on the buoyancy of over 300 British plants.—The small proportion of plants with buoyant seeds or seedvessels.—Their station by the water-side.—The great sifting experiment of the ages.—Summary.

Pages [23-30]

CHAPTER IV

THE LESSON OF THE BRITISH FLORA (continued)

The choice of station of the water-side plant possessing buoyant seeds or seedvessels.—Determined by its fitness or unfitness for living in physiologically dry stations.—In the internal organisation of a plant lies the first determining influence of station.—The grouping of the British strand-plants.—Whilst the Xerophyte with buoyant seed or fruit finds its station at the coast, the Hygrophyte similarly endowed makes its home at the river or pond side.—The grouping of the plants of the river and the pond.—Summary.

Pages [31-39]

CHAPTER V

THE FIJIAN STRAND-FLORA

The inland extension of the beach-plants.—The grouping of the coast-plants.—Their modes of dispersal.—The zone of change.—Summary.

Pages [40-46]

CHAPTER VI

THE TAHITIAN STRAND-FLORA

(From materials supplied mainly by the work of Drake del Castillo)

Lacks the mangroves and their associated plants.—Possesses mainly the plants of the coral beach.—Predominant agency of the currents.—Inland extension of shore-plants.—Summary

Pages [47-50]

CHAPTER VII

THE HAWAIIAN STRAND-FLORA

Its poverty.—Its negative features.—Their explanation.—The subordinate part taken by the currents.—The Oregon drift.—The inland extension of the beach-plants.—Summary

Pages [51-60]

CHAPTER VIII

THE LITTORAL PLANTS AND THE CURRENTS OF THE PACIFIC

The working value of the currents as plant-dispersers.—The relation between the currents and the distribution of shore-plants.—The clue afforded by the American plants.—Two regions of tropical shore-plants, the American and the Asiatic.—America, the home of the cosmopolitan tropical shore-plants that are dispersed by the currents.—Hawaii and the currents.—Summary

Pages [61-75]

CHAPTER IX

THE GERMINATION OF FLOATING SEEDS

Germination in the floating seed-drift of tropical estuaries.—A strain of vivipary.—Abortive germination of seeds in warm seas.—A barrier to plant dispersal.—The borderland of vivipary.—Summary

Pages [76-87]

CHAPTER X

THE RELATION OF THE BUOYANCY OF SEEDS AND SEEDVESSELS TO THE DENSITY

OF SEA-WATER

The general principles concerned.—The subject assumes a statistical character.—Seeds and seedvessels are as a rule either much heavier than sea-water or much lighter than fresh water.—The present littoral plants with buoyant seeds or seedvessels could be equally well dispersed by currents in oceans of fresh water.—Seed-buoyancy has no relation either in the present or in the past to the density of the sea.—Though an accidental attribute, the specific weight of seeds has had a profound influence on plant-distribution.—Summary

Pages [88-98]

CHAPTER XI

ADAPTATION AND MEANS OF DISPERSAL

Nature has never concerned herself directly with providing means of dispersal.—Fleshy fruits not made to be eaten.—Nor “sticky” seeds to adhere to plumage.—Nor prickly fruits to entangle themselves in fur and feathers.—The dispersal of seeds a blind result of the struggle between the intruding Evolutionary power and the controlling influence of Adaptation.

Pages [99-103]

CHAPTER XII

THE CAUSES OF THE BUOYANCY OF SEEDS AND FRUITS OF LITTORAL PLANTS,

WITH ESPECIAL REFERENCE TO THOSE OF THE PACIFIC ISLANDS

The classification of buoyant seeds and fruits.—The first group, where the cavity of the seed or seedvessel is incompletely filled.—The second group, where the kernel is buoyant.—The third group, where there is air-bearing tissue in the seed-tests or fruit-coats.—The buoyant seeds and seedvessels of the littoral plants of the British flora.—Summary

Pages [104-118]

CHAPTER XIII

ADAPTATION AND SEED-BUOYANCY

The question of the operation of Natural Selection.—Are there two principles at work?—The presence of buoyant tissue in the seed-tests and fruit-coats of inland plants, both wild and cultivated.—Useless buoyancy.—The buoyancy of seeds and fruits is not concerned with Adaptation.—Summary.

Pages [119-129]

CHAPTER XIV

THE RELATION BETWEEN LITTORAL AND INLAND PLANTS

Professor Schimper’s views.—Great antiquity of the mangrove-formation.—Problem mainly concerned with the derivation of inland from littoral plants.—Grouping of the genera possessing both coast and inland species.—Scævola.—Morinda.—Calophyllum.—Colubrina.—Tacca.—Vigna.—Premna

Pages [130-139]

CHAPTER XV

THE RELATION BETWEEN LITTORAL AND INLAND PLANTS (continued)

Inland species of a genus developed from littoral species originally brought by the currents but no longer existing in the group.—Illustrated by the Leguminous genera Erythrina, Canavalia, Mezoneuron, and Sophora, and by the Apocynaceous genus Ochrosia.—The Hawaiian difficulty.

Pages [140-154]

CHAPTER XVI

THE RELATION BETWEEN LITTORAL AND INLAND PLANTS (continued)

The Fijian difficulty.—Inland species of a genus possessing fruits not known to have any means of dispersal through agencies now at work in the Pacific.—Pandanus.—Its remarkable distribution in oceanic groups.—To be attributed perhaps to extinct Columbæ or extinct Struthious birds.—Barringtonia.—Guettarda.—Eugenia.—Drymispermum.—Acacia laurifolia.—Conclusions to be drawn from the discussion.—Summary of Chapters XIV., XV., XVI.

Pages [155-169]

CHAPTER XVII

THE STORIES OF AFZELIA BIJUGA, ENTADA SCANDENS, AND CÆSALPINIA

BONDUCELLA

Afzelia bijuga.—The African home of the genus.—The double station of Afzelia bijuga, inland and at the coast.—The nature of the buoyancy of its seeds.—Summary relating to Afzelia bijuga.—Entada scandens.—Its station and distribution.—Darwin’s opinion of the plant.—The dispersal of its seeds by the currents.—Summary relating to the plant.—Cæsalpinia bonducella and C. bonduc.—Their station and distribution.—Their characters in various Pacific groups.—The parents of inland species.—Their dispersal by the currents.—The germination of their seeds.—A dream of vivipary.—The causes of the seed-buoyancy.—Summary of results

Pages [170-197]

CHAPTER XVIII

THE ENIGMAS OF THE LEGUMINOSÆ OF THE PACIFIC ISLANDS

Leguminosæ predominate in tropical littoral floras.—The anomalies of their distribution in the Pacific islands.—They conform to no one rule of dispersal or of distribution.—Strangers to their stations.—The American home of most of the Leguminous littoral plants.—Summary

Pages [198-203]

CHAPTER XIX

THE INLAND PLANTS OF THE PACIFIC ISLANDS

Preliminary Comparison of the Physical Conditions of Hawaii,

Fiji, and Tahiti

Introductory remarks.—The tranquil working of the winds and currents contrasted with the revolutionary influence of the bird.—The Hawaiian, Fijian, and Tahitian groups.—Their surface-areas and elevations.—Their climates.—The mountain climate of Hawaii.—The rainfall of the three groups.—Summary

Pages [204-219]

CHAPTER XX

THE ERAS IN THE FLORAL HISTORY OF THE PACIFIC ISLANDS

The Age of Ferns

The eras 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

Pages [220-230]

CHAPTER XXI

THE ERAS OF THE FLOWERING PLANTS

The Era of the Endemic Genera

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

Pages [231-249]

CHAPTER XXII

THE ERA OF THE ENDEMIC GENERA (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

Pages [250-267]

CHAPTER XXIII

THE ERA OF THE NON-ENDEMIC GENERA OF FLOWERING PLANTS

The Mountain Floras of the Pacific Islands as illustrated by

the Non-endemic Genera

The mountain-flora of Hawaii.—A third of it derived from high southern latitudes.—An American element.—Compared with Tahiti and Fiji.—Capacities for dispersal of the genera possessing only endemic species.—Acæna, Lagenophora, Plantago, Artemisia, Silene, Vaccinium, &c.—Capacities for dispersal of the genera possessing non-endemic species.—Cyathodes, Santalum, Carex, Rhynchospora.—Fragaria chilensis, Drosera longifolia, Nertera depressa, Luzula campestris.—Summary.

Pages [268-288]

CHAPTER XXIV

THE ERA OF THE NON-ENDEMIC GENERA OF FLOWERING PLANTS (continued)

The Mountain-Floras of the Tahitian and Fijian Regions

The mountain-flora of the Tahitian region, as illustrated by the non-endemic genera.—Derived chiefly from high southern latitudes.—Weinmannia, Coprosma, Vaccinium, Astelia, Coriaria, Cyathodes, Nertera depressa, Luzula campestris.—The mountain flora of Rarotonga.—The mountain-flora of the Fijian region, as illustrated by the non-endemic genera.—Weinmannia, Lagenophora, Coprosma, Astelia, Vaccinium, Nertera depressa.—The Fijian Coniferæ.—Dammara, Podocarpus, Dacrydium.—Not belonging to the present era of dispersal.—The age of dispersal of the Coniferæ in the Pacific.—Earlier than the age of Compositæ and Lobeliaceæ.—The first in the Mesozoic period.—The last in the Tertiary period.—Summary

Pages [289-306]

CHAPTER XXV

THE ERA OF THE NON-ENDEMIC GENERA OF FLOWERING PLANTS (continued)

The Age of the Malayan Plants as represented in the Low-level Flora of Hawaii and in the Bulk of the Floras of the Fijian and Tahitian Regions

The Age of Wide Dispersal over the Tropical Pacific

The widely dispersed genera which possess only peculiar species in Hawaii.—Pittosporum.—Reynoldsia.—Gardenia.—Psychotria.—Cyrtandra.—Freycinetia.—Sapindus.—Phyllanthus.—Pritchardia.—Summary.

Pages [307-332]

CHAPTER XXVI

THE ERA OF THE NON-ENDEMIC GENERA OF FLOWERING PLANTS (continued)

The Age of Malayan Plants (continued)

The Age of Wide Dispersal over the Tropical Pacific (continued)

The widely dispersed genera that are as a rule not entirely represented by endemic species in any archipelago.—Elæocarpus.—Dodonæa.—Metrosideros.—Alyxia.—Alphitonia.—Pisonia.—Wikstrœmia.—Peperomia.—Eugenia.—Gossypium.—The last stage in the general dispersal of plants of the Malayan era as illustrated by the widely-dispersed genera having as a rule no peculiar species.—Rhus.—Osteomeles.—Plectronia.—Boerhaavia.—Polygonum.—Pipturus.—Dianella.—Summary.

Pages [333-358]

CHAPTER XXVII

THE ERA OF THE NON-ENDEMIC GENERA OF FLOWERING PLANTS (continued)

The Age of Malayan Plants (continued)

The Age of Local Dispersal

Synopsis of the Chapter given on page 359

Pages [359-410]

CHAPTER XXVIII

THE POLYNESIAN AND HIS PLANTS

Identity of the problems presented by the indigenous plants and the peoples of the Pacific islands.—The food-plants of the Polynesians and the pre-Polynesians.—Their weeds.—The aboriginal weeds.—The white man’s weeds.—Weeds follow the cultivator but are distributed by birds.—The general dispersion of weeds antedates the appearance of the Polynesian in the Pacific.—Weeds of little value to the ethnologist.—Aleurites moluccana.—Inocarpus edulis, Gyrocarpus Jacquini, Serianthes myriadenia, Leucæna Forsteri, Mussænda frondosa, Luffa insularum.—Summary

Pages [411-428]

CHAPTER XXIX

BEACH AND RIVER DRIFT

In the south of England.—On the coast of Scandinavia.—In the Mediterranean.—Southern Chile.—Very little effective dispersal by currents in temperate latitudes.—Cakile maritima.—In tropical regions.—River drift.—River and beach drift of Fiji.—Musa Ensete.—The coco-nut.—River and beach drift of Hawaii.—Comparison of the beach drift of the Old and New Worlds.—Summary

Pages [429-439]

CHAPTER XXX

THE VIVIPAROUS MANGROVES OF FIJI

Rhizophora and Bruguiera

Rhizophora.—Represented by Rhizophora mucronata, Rhizophora mangle, and the Selala, a seedless intermediate form.—Their mode of association and characters.—The relation of the Selala.—Polyembryony.—The history of the plant between the fertilisation of the ovule and the detachment of the seedling.—Absence of a rest period.—Mode of detachment of the seedling.—Capacity for dispersal by the currents.—Bruguiera.—The mode of dispersal.—Peculiar method of fertilisation.—Length of period between fertilisation and the detachment of the seedling.—Mode of detachment of the seedling.—Summary

Pages [440-467]

CHAPTER XXXI

A CHAPTER ON VIVIPARY

The significance of vivipary.—The scale of germinative capacity.—A lost habit with many inland plants.—The views of Goebel.–-The shrinking in the course of ages of tropical swamp areas.—The variation in the structures concerned with vivipary.—Abnormal vivipary.—Summary.

Pages [468-473]

CHAPTER XXXII

THE WEST COAST OF SOUTH AMERICA

The littoral floras of the West Coast of South America.—The Convolvulus soldanella zone of Southern Chile.—The plantless or desert zone of Northern Chile.—The Sesuvium zone of Peru.—The Mangrove zone of Ecuador and Colombia.—The two varieties of Rhizophora mangle, the “mangle chico” and the “mangle grande.”—The floating vegetable drift of the Guayaquil River.—The Humboldt current and the climate of the West Coast of South America.—The advance northward of the arid climatic conditions of the Peruvian sea-border.—The retreat of the mangroves.—Evidence of ancient coral reefs on the coast of Peru.—The shore plants and stranded seed-drift of the Panama Isthmus.—Summary.

Pages [474-501]

CHAPTER XXXIII

SEED-DISPERSAL AND GEOLOGICAL TIME

The shifting of the source of Polynesian plants from the New to the Old World.—The floral history of Polynesia stated in terms of geological time.—The suspension of the agencies of dispersal in later periods.—Parallel differentiation in the course of ages of climate, bird, and plant.—New Zealand.—Insects and bats as agents in plant-dispersal.—The effective agency of sea-birds in other regions.—The observations of Ekstam.—The Spitzbergen controversy.—The efficacy of ducks as distributors of aquatic plants.—Summary

Pages [502-514]

CHAPTER XXXIV

General Argument and ConclusionPages [515-523]
APPENDIXPages [525-605]

LIST OF ILLUSTRATIONS

PLATE.
The Fijian species of Rhizophora[Frontispiece.]
FIGURES.
TO FACE PAGE
Diagrams illustrating some of the causes of seed-buoyancy[111]
Figures illustrating the development of the seed and the germinating process of Rhizophora and Bruguiera[452-453]
Diagrams illustrating the structure of the growing seeds of Barringtonia[574]
Diagram illustrating the prevailing cloud-formations of Mauna Loa[585]
MAPS.
Oceania[12]
The Ocean Currents[61]
Trade routes of the Pacific Ocean (intended to illustrate the distances traversed by floating seeds in that ocean)[66]
The West Coast of South America[474]
Rough plan of the Gulf of Guayaquil[484]

ADDITIONS AND CORRECTIONS

OBSERVATIONS OF A NATURALIST

IN THE PACIFIC

CHAPTER I
INTRODUCTION

The study of insular floras.—Their investigation in this work from the standpoint of dispersal.—The significance of plant-distribution in the Pacific.—The problems connected with the mountain-flora of Hawaii.—The persistence of dispersing agencies at the coast, their partial suspension on the mountain-top, their more or less complete suspension in the forest, and the effect on the endemic character of plants.—The connection between the endemism of birds and plants.—The relative antiquity of plants of the coast, forest, and mountain-top.—The genetic relation between coast and inland species of the same genus.—The ethics of plant-dispersal.—Evolution takes no heed of modes of dispersal.—The seed-stage is the price of Adaptation.

To proceed from the general to the special is the only method of dealing with insular floras. A broad and comprehensive grasp of plant-distribution, such as is only acquired by a life-time of research aided by travel and the handling of large collections, is a necessary foundation for the study; yet in the nature of things such qualifications can be possessed by but a few. To direct an inquiry in the opposite direction, and endeavour to attack the problem of continental floras through the insular floras would result merely in the investigation of a few of the many questions connected with plant-distribution.

The panoramic sketch of the surveyor on the mountain-top aids him in a thousand ways when after months of tedious labour he plots the details in his chart. Without such a panoramic view of the plant-world in his mind’s eye, an observer like myself can only look for guidance to the writings of those who have generalised on the foundations of a far broader experience, such as those of Bentham, De Candolle, Gray, Hooker, Schimper, and others.

It would be quite possible for a botanist possessing a profound general acquaintance with the plant-world to dispense altogether with actual observation and experiment on modes of dispersal. It would be quite possible for him to arrive at conclusions, which, even if they did not always come into line with results of observation and experiment, we should be compelled to prefer. It is only from his more elevated position that a general can follow the course of a battle; whilst the private with his experience confined to a limited area of the field of conflict may form the most erroneous ideas of the progress of the fight. So it is with observers whose employment it is to struggle with the details and secondary principles of plant-distribution, and so it is with the generaliser who has already roughly mapped out the principal features of the main problem.

When Mr. Bentham in 1869, remarking on the paucity of species common to tropical Asia and America, characterised them either as plants wholly or partially maritime and spread by the currents, or as weeds dispersed by cultivation over the warm regions of the globe, he mentioned amongst the plants in the former category, Gyrocarpus jacquini. This tree presents one of the mysteries connected with the Pacific islands; and I don’t imagine that this eminent botanist could have known anything except inferentially as regards the mode of dispersal of its fruits. Yet experiment shows how well founded the inference was, whilst behind it lay a life-time of botanical research.

The author thus approaches the subject of the floras of the Pacific islands rather as a plotter of detail than as a delineator of great designs. However much we may study the means of dispersal, we have behind them the great facts of distribution, serving like the main stations of a trigonometrical survey, and with these we have to make our lesser facts and observations square. One is conscious all the time that much of what seems new in one’s researches has already been foreseen by the generaliser, and that one can do little else than assist in confirming some of his results. This is all that I can lay claim to in this work.

The floras of the islands and coasts of the tropical Pacific are here regarded entirely from the standpoint of plant-dispersal. The fruits and seeds rather than the flowers have been the subject of my investigations; and although there is much to please the eye in the flora of a Pacific island, it was always with a sense of disappointment that I turned away from some pretty flowering plant that failed to present me with its seed. Amongst the wonders of the plant-world rank the Tree Lobelias of the Hawaiian Islands; yet their greatest charm to me lay not so much in their giant-flowers and their arborescent habit as in the mystery surrounding the home of their birth and their mode of arrival in these islands. When I first stood under the shade of the lofty Dammara vitiensis, the Kauri Pine of Fiji, all my interest lay in its cones lying on the ground; and I remember how eagerly I handled my first specimen, and how anxiously I watched its behaviour when experimenting on its capacity for different modes of transport. When a strange plant presented itself on a beach, my first care was to ascertain the fitness of its fruits or seeds for transport by the currents; and all inland plants with fruits likely to attract frugivorous birds were at once invested with a special interest for me.

The mangrove swamps were always great places of interest, and months of my sojourn in the Pacific must have been passed in exploring their creeks and in examining their vegetation. Botanists usually avoid these regions; but the observation of the germination of the Rhizophora fruits on the trees and the inquiries connected with their methods of distribution over the oceans were pursuits so engrossing that I ignored the numerous discomforts connected with the exploration of these gloomy regions. The magnificent mangrove forests of the Ecuador coast of the Pacific will live longest in my memory, though the risks were considerably greater and the discomfort of existence extreme. But the mangrove swamps present us with glimpses into the conditions of plant life during the warmer epochs of the earth’s history, when perhaps the seed-stage was largely dispensed with, whilst an atmosphere, laden with moisture and screening off much of the sun’s light, enveloped most of the circumference of the globe.

The plant world viewed only from the standpoint of dispersal may lack much that is pleasing to the eye, though it abounds with small and great problems fascinating to the reason. Matters of great moment are here involved, and in the case of the Pacific islands they concern not only the source of the oceanic floras, but the story of the islands themselves; whilst behind these there rise up questions of yet deeper import, questions that are bound up with the beginnings of genera and species, and with other mysteries of life on the earth. The distribution of plants presents something more than a problem of means of dispersal, or a problem of station, or a problem of plant migration connected with climatic changes. It is something a great deal more than all three, since it is indissolubly connected with a past, of which unfortunately we know very little. Let us take it to be a question of means of dispersal, and then in imagination transporting ourselves to the Scandinavian coast, let us gather up the stranded West Indian beans of Cæsalpinia, Mucuna, and Entada, that have been drifted there for ages by the Gulf Stream, and lie in some cases semifossilised in the adjacent peat-bog. Was ever dispersal so utterly purposeless as this? Yet here lies a principle of plant-dispersal that is fundamental. We see it in the thistle-seed floating seaward in the wind. Nature never intended its pappus for such an end. It was formed for quite another purpose, yet it aids largely the dispersion of the plant. What can be more significant than that?

Or let us take it to be a matter of station. Given time and the recurrence of the same conditions, with others I once imagined that we could explain most things in plant-distribution, whether of plants at the coast or of plants inland, whether of plants of the alpine peaks or of plants of the plains, or of plants of the river or of the pond. Time, it was held, had long since discounted the means of dispersal, and distribution became merely an affair of station. But the supplanting of many indigenous species of a flora by introduced species is a common story in the plant-world; and such a view needs no further discussion here. Nor is distribution only concerned with plant-migration. Any theory of the origin of alpine floras on tropical mountains will have to explain the presence of the temperate genera, Geranium and Sanicula, not alone on the summits of the mountains of Equatorial Africa and Madagascar, but on the uplands of Hawaii in mid-Pacific, where also are found Ranunculus, Vaccinium, Fragaria chilensis (the Chilian strawberry), and Drosera longifolia.

Taking genera of different stations each in their turn, and following up the clues thus afforded, it would be possible to find support for all the reputable views relating to plant-distribution. The wide range of aquatic plants under conditions that completely change the character of the terrestrial vegetation, such, for instance, as Myriophyllum and Ceratophyllum, might be plausibly attributed to the relative uniformity of the conditions of aquatic life both in time as well as space. The occurrence of Vaccinium on mountain-tops over most of the world, even on the highlands of Samoa, Tahiti, and Hawaii in the Pacific Ocean, would be rightly regarded as evidence of active dispersal of the seeds through the agency of birds from one mountain-summit to another, whether in mid-ocean or in the centre of a continent. The prevalence of the same beach-plants over most of the globe in the same climatic zones would point unmistakably to the predominant agency of currents. But with many plant-genera, some of which range the world, whilst others again may be restricted to a single group of islands in the Pacific, there is often no question either of means of dispersal, or of station, or of plant-migration, and problems of a very different nature are opened up.

When we leave the beach and the mountain-top, the river and the pond, all the troubles of distribution begin; and since but a small proportion of plants in a typical flora belong to these stations, it follows that difficulties will dog our steps with the large majority of the plants. The agencies of dispersal now working around us, the current, the wind, the insect, the bird, and the bat, will explain many of the features of littoral and alpine floras and of the vegetation of ponds and rivers. Here we have in so many cases wide-ranging genera with the means of dispersal ready to hand. We can connect the wide range of Vaccinium with the wide range of birds of the grouse and other families that feed on the berries. We can associate the great areas of aquatic or sub-aquatic genera, like Potamogeton and Sparganium, with the migratory habits of the ducks in the stomachs of which we find their seeds. We can connect the great ranges of beach plants like Ipomœa pes capræ in the tropics, and Convolvulus soldanella in the temperate regions with the currents, and the almost cosmopolitan range of many ferns and lycopods with the winds and other agencies.

When, however, we enter the forests we find genera that are often much more restricted in their areas, and species that are yet more limited in their range. There is very little dispersal going on here. The birds are strange. Their distribution is usually very local. They look lazily down at us from the branches, as they disgorge the seeds and stones of the fruits they have eaten, which cover the ground around. We can almost fancy that they say:—“Our work is done. We rest from the toil of our ancestors. They carried seeds to far-distant Hawaii, Tahiti, and Savaii. Our work is done.” And as we walk through those noiseless forests, where the machinery of species-making is ever in silent motion, we become aware that we are treading one of Nature’s great workshops for the manufacture of species and genera. Outside the forest all is bustle and hurry. We are in the streets, or rather in the distributing areas of the plant-world. We hear the noise of the breaker, the roar of the gale, the cry of the sea-gull, the flapping of a myriad pairs of wings of some migrating host overhead, and we know that the current, the wind, and the bird are actively at work; but their operations are confined mainly to the beach, the mountain-top, the river, and the pond.

Let us take a well-wooded Pacific island several thousand feet in height. We find on its beaches the same littoral plants that we have seen before on the tropical shores of Malaya, of Asia, of Africa, and of America. We find in its ponds and rivers the same species of water-plants, such as Ceratophyllum demersum, Ruppia maritima, and Naias marina, that are familiar to us in the cool and tepid waters of much of the globe. On its level summit, if it remains within the clouds we find in the boggy ground, where Sphagnum thrives, genera that are represented in Fuegia, New Zealand, and the Antarctic islands, such as Acæna, Lagenophora, and Astelia, and the world-ranging Drosera longifolia. In other elevated localities we find Ranunculus, Geranium, Sanicula, Artemisia, Vaccinium, and Plantago, chiefly genera of the temperate regions of the northern hemisphere; whilst there are also found Gunnera, Nertera, and Uncinia, all hailing from the south and belonging to the Antarctic flora characterising all the land-area around the globe in the latitude of New Zealand and Fuegia. The Hawaiian species of Nertera and of Uncinia occur also in New Zealand, and the first-named is found also in Tristan da Cunha and in South America. In the Hawaiian uplands there is also to be seen Deyeuxia, a genus of grasses found in the Tibetan highlands and in the Bolivian Andes at elevations of 16,000 to 19,000 feet; and the same species that exists in Australia may be found in the mountains of Hawaii. Here also, both in Hawaii and Tahiti, occurs Luzula campestris.

In making the foregoing remarks on the alpine plants of a Pacific island, I have had Hawaii in my mind, but we find the elements of a similar widely-distributed mountain-flora in the less lofty peaks of Tahiti and Samoa, and traces even in Fiji, where the mountains, however, have only a moderate elevation. But the point I wish to lay stress on is the cosmopolitan yet temperate character of the mountain-flora of an island lying in the midst of the tropical Pacific. As he shifts his station on this mountain-summit, the observer might at different times imagine himself in the Sierra Nevada of California, on a Mexican tableland, on a peak of the Andes, or in the lowlands of Fuegia. Other plants that I have not mentioned, such as Coprosma, would bring back to him New Zealand. He might even be on a mountain-top in Central Africa, or on a Madagascar plateau; whilst in the boggy region of an elevated Hawaiian tableland he would meet with not only the physical conditions, but also several of the plants found on the higher levels of Tristan da Cunha.

It is, however, to be noted that although these mountain-tops in the mid-Pacific have been stocked with genera from the four quarters of the compass, the species as a rule are restricted to that particular archipelago. Whilst the beach and the river in most cases possess plants that have very wide ranges over the earth, a good proportion of the species on the mountain-summit are not found elsewhere. This implies a partial suspension of the means of dispersal on the mountain-top, whilst the currents and waterfowl are still actively distributing the seeds of the littoral tree and of the aquatic plant. We here get a foreshadowing of another great principle, or of another line along which Nature has worked in stocking these islands of the Pacific with their plants, a subject concerning which much will be said in later pages.

Hitherto, we have dealt only with a small proportion of the flora, and with but a small portion of the area of the island. We have yet to deal with the intermediate region between the sea-border and the summit of the island, or, in other words, with the forested mountain slopes. This is the home of many of the peculiar species and peculiar genera, both of plants and birds; and it is with this zone that we shall be mainly concerned when we come to contrast the floras of the several archipelagoes of the tropical Pacific. Here the agencies of dispersal have, to a large extent, ceased to act; and the question will arise as to the connection between the endemic character of the plants and the endemic character of the birds. We shall have to ask why this island, after receiving so many plants, ceased to be centres of dispersal to other regions. It is possible that these seeds or fruits have lost their capacity for dispersal; but only a few instances of this change present themselves. Rather it may be supposed that the birds that originally brought the seeds to the island came to stay; and this at once suggests another query as to the cause of the change of habit. I am alluding here not to the plants with minute seeds, such as Sagina and Orchis, which Mr. Wallace, in his Darwinism, regards as capable of being transported by strong winds over a thousand miles of sea; but to those numerous plants found in the Fijian, Tahitian, and Hawaiian forests, where the seeds and “stones” are large and heavy, measuring often as much as a quarter of an inch (6 mm.), and sometimes nearly an inch (25 mm.) in size. The reader will be surprised to learn how little “size” has determined the distribution of seeds and fruits in the Pacific. He will have to appeal to the habits of pebble-swallowing of the Dodo, the Solitaire, the Goura pigeon, the Nicobar pigeon, &c., if he desires to find a parallel in the habits of birds.

It is here assumed that the reader is already acquainted with the principles involved in a discussion of island-floras, principles clearly laid down in the writings of Hooker, Wallace, Hemsley, and others. As a general rule in an island or in a group of islands where there are a large number of plants not found elsewhere, there is also a large endemic element in the avifauna, and where none of the plants are peculiar, endemic birds are either few or wanting. As an example of the first we may mention Hawaii, and Iceland affords an instance of the second. But there is no hard and fast rule connecting the endemic character of the plants and birds of an island with its distance from other regions. Even the small group of Fernando Noronha, lying only some 200 miles off the coast of Brazil, possesses its peculiar birds and its peculiar plants; and we can there witness the singular spectacle, as described by Mr. Ridley, of an endemic bird, a frugivorous dove, engaged in scattering the seeds of endemic plants over the little group. This is the only fruit-eating bird in the islands, remarks the same botanist in the Journal of the Linnean Society (vol. 27, 1891); and “when one sees the number of endemic species with edible fruits, one is tempted to wonder if it were possible that they were all introduced by this single species of dove, or whether other frugivorous birds may not at times have wandered to these shores.” This inter-island dispersal in a particular group of peculiar plants by peculiar birds is a common spectacle in the Pacific. The contrast between the large number of plant-genera possessing fruits that would be dispersed by frugivorous birds and the poverty of fruit-eating birds in the avifauna is well displayed in Hawaii.

The island of St. Helena would seem to offer an exception to the rule that endemic birds and endemic plants go together, since, though its flora possesses a very large endemic element, there are scarcely any endemic or even indigenous birds recorded from the island. We can never know, however, how much of the original fauna disappeared with the destruction of the forests. It would nevertheless appear that but few of the genera possessing peculiar species of plants were adapted for dispersal by frugivorous birds. The lesson to be learned from this island concerns the Compositæ, often arboreous, that constitute the principal feature of its flora. St. Helena retains almost more than any other island evidence of the age of Compositæ which has left its impress on many insular floras; and when we discuss the original modes of dispersal of the endemic Hawaiian genera of the same order we shall look to the flora of this Atlantic island for assistance in the matter. To the age of Compositæ belong the beginnings of several insular floras.

To return to the main line of our argument, it would seem that in a Pacific island there is a constant relation between free means of dispersal and the preservation of specific characters. The ocean-current and the aquatic bird are in our own time actively engaged in dispersing the seeds of shore-plants and water-plants, and we see the same species ranging over the world. On the other hand on the mountain-top the agencies of dispersal are beginning to fail, and as a result many a mountain has some of its species restricted to its higher regions. In the forest zone there has been a more or less complete suspension of the activity of the dispersing agencies, and new genera are formed whilst peculiar species abound. Free means of communication with other regions restrains but does not arrest the differentiating process that is ever in progress throughout the organic world. Isolation within certain limits gives it play.

It is in this connection interesting to reflect that during the differentiation of the inland flora the littoral plants have lagged behind or have remained relatively unchanged. The currents have been working without a break throughout the ages; and the cosmopolitan Ipomœa, that now creeps over the sand of the beach, or the wide-ranging Rhizophora, that forms the mangroves of the coast-swamp, must have witnessed the arrival of the ancestors of several of the endemic inland genera. The swamp-plants of the littoral flora are probably older, however, than the beach-plants which have been recruited from time to time in one region or another of the tropics from the inland flora. Yet as a body the littoral plants have lagged far behind the inland flora. We might thus expect that in a Pacific island, excluding the wind-distributed plants, such as the ferns and the lycopods, the most ancient types of the plants would be found at the coast, the most modern in the forests, whilst the plants of the mountain-summit would represent an intermediate age.

But true as this may be, the composition of a strand-flora is a very complex one. Although, as Prof. Schimper remarks, the mangrove formation is more isolated than the beach formation, and affords evidence of a much earlier separation, the beach-plants as a body are anything but homogeneous in their character. Their physiognomy varies to some extent with the alteration in the characters of the inland flora, changes to which the mangrove formation makes a very slow response. Yet amongst the plants of the beach we find strangely assorted forms that are as ancient denizens of the coast as the mangroves themselves. Take, for instance, Salsola Kali, that thrives alike on a beach in Chile, on the sea-shore in Devonshire, and in the salt-marshes of the interior of Tibet. Then, again, there is a type of littoral plant, of which Armeria vulgaris and Plantago maritima may be taken as examples, which is equally at home on the beach and on the tops of inland mountains. We might in a sense apply the wrecker’s motto,

“What the sea sends and the land lends,”

to the history of a littoral flora. Yet on the other hand the inland flora in its turn receives a few recruits from the littoral flora; and it is the relation between the inland and coast species of the same genus that offers one of the most fascinating studies in the botany of the Pacific Islands.

This introductory chapter may be concluded with a few remarks on what may be termed “the ethics of plant-dispersal.” Not that this is in any way a suitable phrase, but it best expresses my sense of the lack of propriety in some things connected with this subject. It is odd, for instance, that we speak of the dispersal of plants and animals in the same breath, as if the process was in both cases identical. Seeing that from this point of view we judge a plant only by its seeds and fruits, it is apparent that we are following quite a different method than that which we employ in the study of the dispersal of animals. Whilst the zoologist classifies the units of dispersal, the botanist does nothing of the kind; and the two systems of classification are at the outset fundamentally distinct. The student of plant-dispersal thus often finds himself placed in an awkward dilemma. For him a family is a collection of allied genera having similar seeds or fruits and fitted often for the same mode of dispersal. A family like Sterculiaceæ, possessing such a variety of seeds and fruits suitable for very different modes of dispersal, is from his standpoint a collection of dissimilar units. Genera like Commersonia, Waltheria, Kleinhovia, Sterculia, and Heritiera, that he so often meets with in the Pacific Islands, have in these respects frequently very little in common; and yet one of the earliest determining influences in plant-life must have lain in the capacity for dispersal.

Yet chance seems to reign in the processes of plant-dispersal ever going on around us. In the floating seed, in the achene with its light pappus blown before the gale, in the prickly mericarp entangled in the plumage of a bird, in the “stone” of the drupe disgorged or ejected by the pigeon, in the small grain that becomes adhesive in the rain, in the tiny rush-seed enclosed in the dried pond-mud on the legs of some migratory bird, in all these we see the agencies of dispersal making use of qualities and of structures that were developed in quite another connection and for quite another purpose. That such characters have been so to speak appropriated by these agencies is a pure accident in a plant’s life-history. If the evolutionary force had been in operation here, it would have selected some common ground to work on. There would have been some uniformity in its methods, whereas the modes of dispersal are infinite. The qualities and characters that happen to be connected with dispersal belong to a plant’s development in a particular environment. They can never have been adapted to another set of conditions that lie quite outside that environment. There is a relation of a kind between the specific weight of wood and the density of water, and this, in a sense, sums up the connection between a seed and its distributing agencies.

Evolution has never concerned itself directly with means of dispersal. Evolution and Adaptation represent the dual forces that rule the organic world, the first an intruding force, the last a passive power representing the laws governing the inorganic world. To these laws the intruding power has often been compelled to bend, and it has had to pay its price, and sometimes it has succumbed, and sometimes it has turned its defeat into a victory. Nature, so watchful over the young plant, as represented by the seed, is finally compelled to let it go, and dispersal begins where evolution ends, or rather when the evolutionary power fails. The seed-stage itself is the price of adaptation. The death of the individual may also be regarded from the same standpoint. It represents a defeat of the evolutionary force, which, however, has been retrieved by the gift of reproductive power.

CHAPTER II
THE FLORAS OF THE PACIFIC ISLANDS FROM THE STANDPOINT
OF DISPERSAL BY CURRENTS

The initial experiment.—The proportion of littoral plants.—The two great principles of buoyancy.—The investigations of Professor Schimper.—The investigations of the author.—The great sorting process of the ages.—Preliminary results of the inquiry into the buoyancy of seeds and fruits.

In the previous introductory chapter some of the numerous questions affecting insular floras were briefly referred to. I will now ask my reader, if he has had the patience to read it, to consign that chapter for the time at least into oblivion, and to proceed with me to our Pacific island with the intention of investigating its flora from the standpoint of dispersal. We will together take up the subject de novo, after banishing from our minds all preconceptions that we may have possessed.

After having been over the island gathering specimens of all the seeds and fruits, we return to our abode on the beach. But we are puzzled where to begin. The problem presents itself as a tangled skein, and our difficulty is to find an “end” that we can follow along with some chances of success. In our trouble we look around us; and at that moment we see a number of floating seeds and fruits carried by the current past the beach. This presents us with a clue and our investigation begins.

OCEANIA
John Bartholomew & Co., Edinr.

We place all our seeds and fruits in a bucket of sea-water and notice that many of them sink at once. In a few days we look again and observe that many more are at the bottom of the bucket, only a small percentage remaining afloat. We then remark to our surprise that nearly all of the floating seeds and fruits belong to coast plants, those of the inland plants, which indeed make up the great bulk of the flora, having, as a rule, little or no buoyancy. After a lapse of weeks and months the seeds and fruits of the coast plants are found to be still afloat. In the results of this experiment we see the work of the ages. There has been, in fact, a great sorting process, during which Nature has “located” the plants with buoyant seeds or seed-vessels at the sea-coast, placing the others inland. This is the clue that we shall follow up during many chapters of this book; and having in this manner introduced the reader to the subject, I will now refer to the general results of my investigations in this direction in the Pacific Islands.

In Fiji there are about eighty littoral plants out of a total of at least 900 species of indigenous flowering plants, that is to say about nine or ten per cent. ([Note 1]), the littoral grasses and the sedges being with one or two exceptions excluded. These shore plants belong to the sandy beach and to the coast swamp, and most of them are distributed over the tropical shores of the Indian and Pacific Oceans, whilst not a few occur on the coasts of tropical America. They form the characteristic plants of the coral atoll, and many of them have long been known to be dispersed by the currents. From the list given in [Note 2] it will be seen that these eighty species belong to about seventy genera. Nearly all of them (95 per cent.) possess seeds or seed-vessels that float at first in sea-water; whilst three-fourths of them (75 per cent.) will float unharmed for two months and usually much more, and several of them will be found afloat after a year or more, being still capable of reproducing the plant ([Note 3]).

The prevalence in the Fijian strand-flora of Leguminosæ, which are included in my list under the divisions Papilionaceæ, Cæsalpinieæ, and Mimoseæ, is very significant. They make up about 29 per cent. of the total. Excluding weeds and a few other introduced plants, there are some fifty species known from the Fijian Islands, and of these almost half belong to the littoral flora, which as we have seen constitutes only a fraction (one-tenth) of the whole flora. If we regard the genera, we find that out of some thirty Leguminous genera twenty are littoral and in most cases exclusively so. This conspicuous feature in the constitution of the strand-flora is of prime importance as concerns the question of adaptation to dispersal by currents, since nearly all the Leguminosæ with buoyant seeds offer themselves as defiant exceptions to any such law.

I will now contrast the Fijian inland flora with that of the coast from the point of view of the buoyancy of the seed or fruit, according as it presented itself for possible dispersal by currents. Rather over a hundred plants were experimented upon ([Note 4]). After excluding some introduced plants there remain some ninety species belonging to about sixty genera, and of these quite 75 per cent. sank at once or in a few days. I may add that all kinds of fruits are here represented, the capsule, the achene, the coccus, the berry, the drupe, &c. Of the buoyant residue few possess seeds or fruits that will float uninjured for any length of time. Not many gave indications directly in opposition to the principle that whilst the seeds or fruits of shore-plants generally float, those of inland plants usually sink, since as pointed out in [Note 5] most of the difficulties are removed during the subsequent developments of the principle discussed in the later pages of this work or are to be explained on other grounds stated in the note.

We pass now from Fiji as typical in its flora of the Western Pacific to Tahiti as representing in its flora the more strictly oceanic groups of Eastern Polynesia. In the Tahitian region, which is taken as including in a general sense the Society Islands, the Marquesas, and the Paumotus, there are only between 50 and 60 littoral plants, excluding the occasional additions from the inland flora. As indicated by the letter T preceding the species in the list of Fijian shore plants, nearly all are to be found in Fiji, and the few not yet recorded from that group, which I have referred to in the remarks following the list, will probably be found there by some subsequent investigator. In Tahiti also between 75 and 80 per cent. of the strand plants have seeds or seedvessels that float for months; and here also Leguminosæ predominate, forming about 30 per cent. of the total. A conspicuous negative feature in the Tahitian strand-flora is concerned with the absence of the mangroves and their numerous associated plants, which together form the mangrove formation in Fiji. This remarkable character in the distribution of shore plants in the Pacific is discussed in [Chapter VI].

Not having visited Tahiti, I can only deal inferentially with the inland plants, as in the case of the strand-flora. Here also the plants are in the mass Fijian in a generic and often in a specific sense, and there is no reason to believe that the principle involving the non-buoyancy of the seeds or fruits of inland plants does not as a rule apply to Tahiti as well as to Fiji.

The Hawaiian Islands, standing alone in the North Pacific, form a floral region in themselves, a region that is the equivalent not of one group in the South Pacific, such as that of Fiji or of Tahiti, but of the whole area comprising all the groups extending from Fiji to the Paumotu Archipelago. Lying as it does mainly outside the zone of influence of the regular currents that would bring the seeds of tropical plants to its shores, Hawaii possesses a strand-flora that is meagre in the extreme. Not only does it lack the mangrove formation so characteristic of Fiji, but it lacks also many of the plants of the beach formation that are found both in Fiji and in Tahiti, plants that give a peculiar beauty to the reef-girt beaches all over the South Pacific. Its poverty is sufficiently indicated in the number of its species, thirty in all, barely more than half of the number found in Tahiti, and not much over a third of those occurring in Fiji. Though coral reefs with their accompanying beaches of calcareous sand are relatively scanty, the characteristic littoral plants have not been numerous enough to hold their own against intruders from the inland flora, and endemic species have taken a permanent place amongst the strand plants. The Hawaiian strand-flora has thus quite a facies of its own, and it will be found discussed in [Chapter VII.], whilst a list of the plants is given in [Note 28]. It will thus not be a matter for surprise that the littoral flora of Hawaii follows the principle of buoyancy only in a modified degree. It is true that about two-thirds of the species of the present beach flora possess seeds or seed-vessels that float for months; but since there are reasons for believing that several of them are of aboriginal introduction, this proportion is reduced to a third. In the list of the Fijian shore plants given in [Note 2], those occurring also in Hawaii are preceded by H.

When we look to the Hawaiian inland flora for indications respecting the principle of the non-buoyancy of the seeds or seed-vessels of inland plants, we find that so far as it has been there tested this principle receives fresh support from the plants growing on the slopes of the Hawaiian mountains. Although the author was only able to sample the inland flora, we have in the list given in [Note 6] all kinds of plants, from the forest-tree to the herb, and most varieties of fruits. Excluding a few introduced plants, there are in this list about fifty species of indigenous plants belonging to about forty genera. Of these plants quite 80 per cent. possess seeds or fruits that sink either at once or in a week or two. Of the “buoyant” residue very few have seeds or fruits that will float for months. These apparent exceptions to the principle are in great part capable of being explained on the grounds referred to in [Note 5] in connection with the Fijian inland plants; and I have alluded to them in [Note 7].

The littoral flora of Fiji is essentially Malayan and Asiatic, and for our purpose is eminently typical. Its plants are found far and wide on the tropical coasts of the Old World, and sometimes also in the New World. In more than half the species we are concerned with the dispersal by currents of more or less dry indehiscent fruits that range usually in size from a marble to a cricket-ball, as illustrated by those of Hernandia peltata and Barringtonia speciosa, whilst with most of the rest the currents distribute large seeds, several of which are Leguminous, as in the case of Mucuna, Cæsalpinia, and Entada, with others of the Convolvulus type, as in the instance of Ipomœa pes capræ. It is remarkable that in selecting plants with buoyant seeds or seed-vessels for a station at the coast Nature has generally ignored those with very small seeds. When such small seeded plants, as Sesuvium portulacastrum, occur on the beach, the seeds have as a rule no buoyancy. Pemphis acidula is, however, an exception; but its case is a very rare one. It will be established in the next chapter that the non-buoyancy of small seeds is generally true also of plants growing by the river or by the pond.

The point at which we have arrived in our inquiry concerning the general collection of seeds and seed-vessels that we placed in sea-water is that the plants with buoyant seeds or seed-vessels have been for the most part “located” at the coast. But if we look a little more closely at the sunken and floating seeds, we find that in the same genus there are species with seeds or seed-vessels that sink and species with those that float. We look again and then perceive that the same general principle is true of different species of the same genus growing inland and at the coast. We learn now that as a rule when a genus possesses both littoral and inland species, the seeds or fruits of the former float in sea-water for a long time, whilst those of the latter have little or no floating power. But we have yet to examine the structure of the coverings of the buoyant seed or fruit; and we shall then discover that the different behaviour in water is often associated with corresponding structural differences of a striking character. The structural causes of buoyancy are dealt with in [Chapter XII.]; and we will now content ourselves with enunciating the second principle that in a genus comprising both coast and inland species, only the coast species possess buoyant seeds or seed-vessels.

The important principle above indicated was not altogether new to me, as is shown in the next chapter. But it was new in the case of the floras of the Pacific Islands. When it first presented itself in Hawaii I was engaged in trying to find a connection between the inland and littoral species of Scævola; and its discovery led me to form a plan worthy almost of Don Quixote, namely, to cultivate the beach species of Ipomœa, Scævola, and Vitex in the interior with the hope of finding them converted into inland species when I returned to Hawaii after a lapse of years. Little matters often determine a career, and for a while my future movements and probably the remainder of my life were largely centred around my interests in the well-being of Scævola Kœnigii. The scheme was actually undertaken, and I had fixed on a little plot of land at the foot of the mountains rising behind Punaluu in Kau. The transaction was on the point of completion when the owner changed his mind and the plan fell through. Subsequent observation and reflection have led me to believe that in most cases no connection exists between the littoral and inland species of a genus; and I have dwelt on this incident merely to show the importance that I rightly attached to this distinction, whilst misinterpreting its meaning.

But to return to my own investigations. Had I indeed read more carefully Professor Schimper’s work on the Malayan strand-flora, this subject would have been found discussed by an observer far abler than myself, though from a very different standpoint, that of Adaptation and Natural Selection. He points out (pp. 179-182) that with a number of these tropical genera possessing both littoral and inland species, such as Barringtonia, Calophyllum, Clerodendron, Cordia, Guettarda, and Terminalia, greater buoyancy of the fruits of the shore species is associated with certain structural characters in the fruit-coverings, whilst with the inland species, where the floating power of the fruits is either much diminished or entirely absent, these structural characters are either less developed or lacking altogether.

The question of structure and the debateable matters concerned with it are treated at some length in Chapters [XII.] and [XIII.], and Professor Schimper’s views are there given. I will content myself with remarking that the genus Terminalia was especially studied by him in this respect. He tested the buoyancy of the fruits of ten species, and found that the flotation period varied from nothing to 126 days and more. By far the best “floaters” were the fruits of Terminalia Katappa, the only littoral species tested, all the others being inland species with less buoyant fruits, and diminished ranges, some of the fruits sinking at once, whilst the others sank usually in a few days or in a few weeks. It was also ascertained that, although the buoyant tissue in the fruit-coats varied in amount generally with the floating-powers, it was rarely absent altogether in the inland species, a very significant conclusion, as will subsequently be pointed out.

Several other striking examples of this principle came under my notice in the Pacific, and perhaps the most significant is that of Scævola, a genus of the Goodeniaceæ, confined mainly to Australia and the Pacific islands, but possessing also a littoral species, S. Kœnigii, that is found on tropical beaches all round the globe. It is associated in both Hawaii and Fiji with inland species, none of which are common to the two archipelagoes, and in the case of the Hawaiian species not found outside the group. All the species have fleshy drupes, both coast and inland plants, the “stone” in the littoral species possessing a thick covering of buoyant tissue, which is absent or but slightly developed in the inland species. The fruits of the shore species float for many months; whilst those of the inland species experimented on by me (S. Chamissoniana and S. Gaudichaudii in Hawaii, and S. floribunda in Fiji) sank at once or within a few hours. Here we are only concerned with the difference of buoyancy between inland and littoral species. The several other questions involved concerning this genus will be dealt with later on in this work.

The genus Morinda offers another good example of this principle. It includes one widely-spread littoral species (M. citrifolia), found not only in all the Pacific archipelagoes, but also over much of the tropics. It is associated in all the large groups with one or more inland species, some of which are endemic and others more generally distributed. The littoral species displays in its pyrenes a singular air-cavity, the nature of which is discussed in [Chapter XII.], which endows them with great floating powers. This cavity is not found in inland species, and the pyrenes have in consequence no floating power (see [Note 8]).

Calophyllum Inophyllum, an Old-World littoral tree, spread far and wide over the Pacific islands, has very buoyant fruits. In the groups of the South Pacific it is associated with inland species that are commonly found in the forests, namely, C. spectabile and C. Burmanni, the fruits of both of which, according to my observations in Fiji, have limited floating powers, sinking after periods varying from a few days to four weeks, and lacking in great part the buoyant coverings of the littoral species. Professor Schimper obtained similar results with inland species from other regions ([Note 9]).

The fruits of the two Fijian coast trees, Barringtonia speciosa and B. racemosa, possess great floating powers; whilst those of an undescribed species that I found in the mountains of Vanua Levu sink at once. Another Fijian inland species (B. edulis, Seem.) that is often planted, has fruits that float heavily for about a month. This difference in buoyant powers is also associated with characteristic differences in the structure of the fruits. It would be interesting to learn what floating capacity belongs to those of the Samoan endemic species (B. samoensis, Gray). Professor Schimper’s observations on the genus in the Malayan region point in the same direction, but more than one difficulty awaits its solution in the re-examination of the genus. He says, however, that B. excelsa, Bl., a Malayan species, sometimes cultivated and growing both inland and at the coast, has fruits that floated for one hundred days after drying (p. 173).

A striking instance of this principle is afforded in the case of the two Fijian species of Tacca, the wide-ranging littoral species, T. pinnatifida, where the seeds float for several months, and the inland species, T. maculata, Seem., found also in Australia and Samoa, where the seeds sink at once or in a few days. The seeds of the shore plant owe their buoyancy to the spongy tissue in their coverings, which is either absent or much less developed in those of the inland species. This point might also be determined for the new Samoan inland species described by Reinecke, the German botanist, as T. samoensis.