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.

November 8th, 1905.