MY object in writing this book is primarily to call attention to some of the many questions which are raised by an enquiry into the relative antiquity of existing plants, and to illustrate the nature of the evidence afforded by the records of the rocks. One may agree with the dictum, 'There is but one art—to omit,' but to practise this art is often a difficult task. While fully conscious of the incompleteness of the treatment of the subjects dealt with in these pages, and of defects in the method of presentation, I hope that I may succeed in attracting some of my readers who are already interested in living plants to the study of plants of former ages.

I am greatly indebted to my colleague Dr C. E. Moss for reading the proofs and for many valuable suggestions. I wish to thank Mr and Mrs Clement Reid, Prof. MacDougal of the Arizona Desert Laboratory, Prof Campbell of Stanford University, Prof F. H. Knowlton of the United States National Museum, Washington, Mr A. G. Tansley, Prof Yapp, and Mr W. R. Welch for photographs which they have allowed me to reproduce. As on many previous occasions, I am indebted to my wife for contributing drawings.

A. C. SEWARD.

Botany School, Cambridge.
July 1911.

The numbers in brackets interspersed in the text refer to the Bibliography at the end of the volume.