NORTH CAROLINA STATE UNIVERSITY LIBRARIES S02842957 This book is due on the date indicated unless recalled by the Libraries. Books not returned on time are subject to replacement charges. Borrowers may access their library accounts at: http://www.lib.ncsu.edu/ads/borrow.html AGE AND AREA CAMBJIIDGE UNIVERSITY PRESS C. F. CLAY, Manager LONDON : FETTER LANE, E.G. 4 LONDON : H. K. LEWIS AND CO.. Ltd., 136, Gower Street, AV.C. I LONDON: WHELDON AND WESLEY. Ltd.. 28. Essex Street, Strand. W.C. 2 NEW YORK: THE MACMILLANCO. BOMBAY \ CALCUTTA \ MACMILLAN ANDCO.. Ltd. MADRAS J TORONTO : THE MACMH,LAN CO. OF CANADA, Ltd. TOKYO : MARUZEN-KABUSHIKI-KAISHA ALL BIGHTS KESER\-ED AGE AND AREA A STUDY IN GEOGRAPHICAL DISTRIBUTION AND ORIGIN OF SPECIES BY J. C. WILLIS M.A., Sc.D., Hon. ScD. (Harvard), F.R.S. European Correspondent, late Director, Botanic Gardens, Rio de Janeiro WITH CHAPTERS BY HUGO DE VRIES, F.M.R.S. H. B. GUPPY, M.B., F.R.S. Mrs E. M. REID, B.Sc, F.L.S. JAMES SMALL, D.Sc, F.L.S. [These authors are not committed, by writing these chapters, to the support of all the doctrines here advanced] CAMBRIDGE AT THE UNIVERSITY PRESS 1922 ^ ,% ^y^h a 4 PREFACE Some thirty years ago, a pupil of the strictest school of natural selection, and enthusiastic in my belief in its principles, I set out upon a course of independent observation of nature. Ten years of such work convinced me that a simpler explanation of phenomena was always to be found, and one that seemed more in accordance with the facts; and I endeavoured—with what success this book will show—to free myself from the trammels of the natural selection theory, and to work as if I had found myself in another planet where scientific investigation was just begin- ning. Stationed in one of the best centres in the tropics (where the phenomena of distribution are more impressive than in Europe), badly handicapped in laboratory work by a serious accident, and finding my chief pleasure in travelling about the world to see its vegetation—I took up the study of distribution, in which I had always taken much interest. Here, as elsewhere, it was soon evident that the current theories pro^'ided an explanation that was not only unnecessarily complex, but one that did not explain. As one of my critics words it, "for some reason the plant has advantages which enable it to spread"; and beyond that point we cannot go. Gradually it became clear to me that plants spread very slowly, but at an average rate determined by the various causes acting upon them, so that age forms a measure of dispersal when one is dealing with allied and similar forms. Age as an explanation of spread is enormously simpler than natural selection, and that it is probably valid is shown by the way in which it can be used for prediction. An opponent re- marks that "it is too simple to be true," but this very simplicity seems to me a strong reason in favour of its adoption, at any rate as a preliminary hypothesis. Of two explanations take the simpler, is an old rule, and as Hooker has said, "no speculation is idle or friiitless, that is not opposed to truth or to probability, and which, while it coordinates a body of well-established facts, does so without violence to nature, and with a due regard to the vi PREFACE possible results of future discoveries." To find explanation of the facts of distribution under the current theories has always seemed a very hopeless task, and any hypothesis that offers a way out should at least receive attention. No hypothesis can, after all, alter the facts, though it may show ways in which to accumulate new ones. In the second part of the book, I have pushed my hypothesis to what seem to me its logical conclusions, conclusions which are sometimes subversive of received opinions. To be compelled to re-examine the bases upon which those opinions are founded will do science no injury, however. While the defects of the book are my own. I owe what is good in it very largely to the constant help, advice, and criticism of many friends, among whom I would specially mention Dr Hugo de Vries, Dr H. B. Guppy, Mrs E. M. Reid, and Prof. James Small, all of whom have also contributed chapters to the work. To these four I must add my friend Mr G. Udny Yule, to whose trained mathematical skill I owe much useful help and criticism. Prof. J. Stanley Gardiner has helped me very greatly in the work upon animals. In particular he was so kind as to obtain for me the help of Dr Hugh Scott, who spent hours with me in counting beetles, Mr E. Meyrick, F.R.S., who gave me figures for dis- tribution of Micro-Iepidoptera, Mr G. C. Robson, and Dr W. T. Caiman, F.R.S. To the criticism of Prof. E. S. Prior, A.R.A., I largely owe the present simplified form of the book, and its freedom from technical terms; he was also so kind as to obtain for me the aid of Dr W. D, Lang. References to literature, and other valuable help, I owe to Sir David Prain and Mr S. A. Skan at Kew, Mr G. Goode, ]\I.A,, at the University Librarj^ IVIiss Taylor at the Balfour Library, and others, whilst I am also deeply indebted for help and criticism to (the late) Dr E. A. N. Arber, Mrs Agnes Arber, Prof. Margaret Benson, ^Ir E. Breakwell, Dr W. B. Brierley, Dr N. L. Britton, Dr J. Brownlee, Mr J. Burtt- Davy, Dr L. Cockayne, (the late) Mr R. \V. Davie, Mr C. E. Foweraker, Mr E. G. Gallop, Prof. R. Ruggles Gates, Dr B. Daydon Jackson, (the late) Dr A. Lofgren, Dr D. T. MacDougal, Dr J. H. Maiden, Miss E. R. Saunders, Dr D. H. Scott, Prof. A. C. Seward, Mr A. M. Smith, Dr Norman Taylor, Dr R. J. PREFACE vii TiUyard, Prof. A. Wall, Dr J. E. B. Wanning, Prof. D M S Watson, and many others. That I have been able to carry out this work at all I to owe the labours of generations of systematists, botanical and zoological, foremost among whom, inasmuch as the hypothesis of Age and Area was originally founded upon their work, I must place my predecessors in Ceylon, G. H. K. Thwaites and Henry Trimen. I must also specially mention Sir Joseph Hooker, as this work forms a continuation of his labours of the fifties. Last, but not least, I am deeply grateful to my wife, and to my relatives, Mrs and Miss Steel, Vo^'r much help ungrudgingly given. For illustrations I am much indebted for loan of blocks to the Royal Society, and to the Editors of the Annals ofBotany, Nature, and Nezv Plnjtologist: also to my daughter Margaret, who made the drawings from which all, except those on pp. 125, 153, 173, 241 and 242, were jDrepared. J. C. WILLIS. Cambridge, 4 April, 1922. CONTENTS PART I. THE PRESENT POSITION OF AGE AND AREA CHAP. PAGE I. Introductory 1 II. The Dispersal of Plants into New Areas . 10 III. The Introduction and Spread of Foreign Species 21 IV. Acclimatisation 29 V. Causes which favour or hinder the Dis- persal OF Species 32 VI. Age and Area 54 VII. Age and Area {contd.). Confirmation by Prediction 66 VIII. Age and Area {contd.). Invasions ... 70 IX. Objections to the Hypothesis ... 84 PART II. THE APPLICATION OF AGE AND AREA TO THE FLORA OF THE WORLD, AND ITS liSIPLICATIONS X. The Position of the Age and Area Theory 101 By H. B. GUPPY, M.B., F.R.S. XI. The Further Extension of the Application of Age and Area 107 XII. Size and Space 113 XIII. Age and Area, and Size and Space, in the Compositae 119 By Jajies Small, D.Sc, F.L.S. CONTENTS CHAP. XIV. Age and Area from a Palaeobotanical Standpoint 137 By Mrs E. M. Reid, B.Sc, F.L.S. 148 XV. Endemism and Distribution: Species . 169 XVI. Endemism and Distribution : Genera . XVII. The Monotypic Genera, and Genera of Larger Size ...... 185 XVIII. The Hollow Curve of Distribution 195 XIX. Applicability of Age and Area to Animals 200 XX. The Origin of Species .... 204 XXI. Age and Area and the Mutation Theory 222 By Hugo de Vries, F.M.R.S. XXII. Geographical Distribution: General . 228 List of Literature .... 247 Index 253 The illustrations on pp. 56, 66, 76, 78, 79, 80, 153, I owe to the courtesy of the Editor, Annals of Botany. PART I THE PRESENT POSITION OF AGE AND AREA CHAPTER I INTRODUCTORY 1 HE existing distribution of a plant (or animal) upon the surface of the globe, which is often a very complex phenomenon, is due to the interaction of very many factors. Sometimes they are inherent to the plant itself, sometimes they are incidental to its surroundings, sometimes they partake of both qualities. At times they may be active, at others ver}^ active, and at some periods, or in some places, they may be more or less quiescent. One pulls in one direction, another in another. As a plant spreads from the place in which it originally commenced, therefore, it comes under an ever-varying pull, causing it to spread more or less rapidly, or at times not at all, according to the different and ever-altering combinations of these factors—different climates, different soils, different groups of plants that occupy the soil, presence or absence of such barriers as are offered l)y mountains, seas, changes of climate, and many other things.