VI 



PREFACE 



Now, after the lapse of seventeen years, it has been possible to state the 

 biological argument more fully in the present volume, strengthened by many 

 new facts. The First Part (pp. 1-254) deals with the general theory. The 

 Second Part (pp. 255-657) is taken up with a detailed statement of the facts, 

 together with comparison of the constituents of the several phyla inter se. 

 The Third Part (pp. 658-717) is devoted to general comparisons and con- 

 clusions. The attempt has been made to work in the results of Palaeonto 

 logical research with those of the comparative analysis of living forms. The 

 enquiry has related to all the characters, both vegetative and propagative, of 

 the sporophyte generation : these include the external form, the embryogeny, 

 and anatomical features, and especially the structure and development of 

 the Spore-producing members, while the characters of the gametophyte 

 have also been taken into account. It is found that the conclusions 

 arrived at are supported by general convergence of the lines of evidence 

 derived from all of these sources. 



The method adopted in the preparation of this work has been to 

 examine not only the mature structure, but also the development of the 

 organisms, and of their several parts. While fully utilising the results of 

 Palaeontological and anatomical study, considerable weight has throughout 

 been given to the facts of the individual development : sometimes the latter 

 appear to oppose the former. It is not held that the ontogenetic history 

 will always serve as an infallible guide, and opportunity has been taken 

 to point out that conclusions based upon it are liable to be overruled by 

 the results of wide comparison (pp. 159, 636, and 660, footnote). But it 

 is felt that in much of the recent work on Pteridophytes, and especially 

 where fossil comparisons come in, the arguments from individual develop- 

 ment have been accorded less than their due share of attention. 



I have made no attempt to give comprehensive or complete biblio- 

 graphical references : from Campbell's Mosses and Ferns and from other 

 sources such references can readily be obtained. But wherever a quotation 

 is made, or where a substantial body of information derived from another 

 author has been embodied in the text, the reference is fully given. While 

 thus acknowledging my indebtedness to those whose work is published, 

 I desire also to record the continuous personal help so willingly given by 

 three friends and colleagues, who have all allowed me the use of unpub- 

 lished drawings and facts. Mr. Kidston's peculiarly exact knowledge has 

 greatly strengthened and amplified the Palaeontological statements, while 

 Dr. Lang and Mr. Gwynne-Vaughan have given me throughout the 

 assistance of friendly criticism, and the support of their special knowledge 

 of certain branches of the matter in hand. 



In conclusion, I am well aware that the chief question dealt with 



