INTRODUCTION TO VOLUME II 



As some years have necessarily elapsed since the publication of the First 

 Volume of this Work, and since the volumes will be on sale separately, 

 it seems desirable to offer a brief summary of the contents of the First 

 Volume which shall serve as an introduction to the Second, and so to link 

 the whole Work together into a coherent whole. It has been shown in 

 Chapter ill of Vol. i that those arrangements of the constituent Families 

 of the Filicales which have their place in current Botanical Literature appear 

 to be marked by chance rather than by considered method, and are often 

 wanting in suggestion of phyletic, that is evolutionary, sequence. This is 

 believed to have been a natural consequence of the insufficiency of the, 

 foundations upon which such systems have hitherto been based. Accordingly, 

 a definite attempt has been made to extend those foundations by using 

 wider comparisons, and by seeking new criteria for that purpose. The result 

 has been that twelve leading characteristics of Ferns have been selected to 

 serve as a broad basis for their comparison with a view to the phyletic 

 seriation of the Class — this being the end aimed at in any Natural Classifica- 

 tion. The number of such criteria used by different authors may vary, and 

 will probably be added to by later writers. Those to be used here are these: 

 (i) The external morphology of the shoot. 



(2) The initial constitution of the plant-body as indicated by 

 segmentation. 



(3) The architecture and venation of the leaf 



(4) The vascular system of the shoot. 



(5) The dermal appendages. 



(6) The position and structure of the sorus. 



(7) The indusial protections. 



(8) The characters of the sporangium, and of the spores. 



(9) The spore-output. 



(10) The morphology of the prothallus, 



(11) The position and structure of the sexual organs. 



(12) The embryology of the sporophyte. 



Each of these criteria has been examined critically in Ferns at large, and 

 the scope of variation noted in respect of each. The extreme variants have 

 been checked according to the fossil record, so that it should become 

 possible with some degree of confidence to assert for each criterion which of 

 its variants are to be held as relatively primitive, and which as relatively 

 derivative. The consequences of this procedure in respect of the several 

 criteria have been found to work out as follows: 



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