vi PREFACE 



was advanced to account for their "diplobiontic" mode of life in relation to 

 the passage of green organisms from an aquatic to a terrestrial habit. A critic 

 of that volume once said, with some degree of justification, that the theory- 

 was out of date before it was published: and so it was as regards any general 

 application to diplobiontic life, for this had already been demonstrated in 

 Algae which had not invaded the land. Still this fact does not by any means 

 rule out some close biological relation between alternation and that amphibial 

 life which the Archegoniatae show (see Chapter XLix). The whole subject 

 is still open for further enquiry, and welcome light is being shed upon it by 

 the writings of Svedelius, and others. 



Incidentally the composition of the book on The Origin of a Land Flora 

 demonstrated that the facts and methods current at the opening of the 

 present century could not suffice for any full evolutionary treatment of the 

 Class of the Filicales. Not only were further details necessary for an adequate 

 comparison of Eusporangiate Ferns, but more particularly the tangled 

 problem of the evolutionary lines of the Lepto^porangiate Ferns was still 

 too obscure in 1908 for any coherent treatment. Their phyletic relations 

 were hardly more than hinted at in the Land Flora, pending further research. 

 It was necessary in the first instance to widen the basis of comparison by the 

 introduction of new criteria, each treated critically, so as to distinguish 

 archaic features from those held to be of more recent origin. The conclusions 

 thus attained were checked so far as possible according to the palaeontological 

 evidence. The results of such study were first published in a series of 

 Memoirs, l-viii, in the Annals of Botany (1910-1923): and these supplied 

 the material for Vol. I of this work. In Vol. II the phyletic method based 

 on this wider comparison was applied to the relatively primitive Ferns : while 

 the present Volume aims at a like phyletic treatment of the great mass of 

 advanced Leptosporangiate Ferns. 



In a sense then this work may be held as opening a fresh period in the 

 Classification of Ferns. It is the sincere hope of the author that it may 

 stimulate further enquiry, suggest the use of still other criteria of comparison, 

 and perhaps lead finally to other conclusions than those here adopted. 

 Readers who know the literature of the subject will be well aware that such 

 general statements as are embodied here are really a summation of results 

 from the widest possible sources, supplied by a host of investigators: and 

 happily the spirit of enquiry is as active as ever. Advance rather than 

 finahty has been the aim of the author in summing up the results: for, 

 repeating again the words of Stevenson used as a motto to the First Volume, 

 "To travel hopefully is a better thing than to arrive." 



F. O. BOWER 



RiPON 

 1928 



