GENERAL RESULTS— PTEROPSIDA 645 



same phylum with the Ferns appears indisputable and 

 needs no detailed proof. In all characters in which 

 these early Seed-plants approach the Cryptogams, 

 whether in habit, anatomical structure, the morphology 

 of the sporophyll, or the nature of the microsporangiate 

 fructification, it is with the Ferns alone that affinity is 

 shown. The stock from which they were derived is 

 still unknown, and may well have differed widely 

 from any group of Ferns with which we are familiar, 

 but there is no longer any room for doubt that it had 

 far more in common with the Ferns than with any other 

 race of Pteridophytes. 



We have to conceive of the Pteridosperms as a vast 

 plexus of varied forms, of which the few types as yet 

 adequately known can give but a very imperfect idea. 

 For example, we know nothing as yet of the structure 

 of those Pteridosperms which, like Aneimites or 

 Pecopteris Pluckeneti (pp. 465, 466), bore seeds of the 

 bilateral type, resembling those of Cordaiteae. Our 

 detailed knowledge is limited at present to the two 

 series, Lyginodendreae (Chap. X.) and Neuropterideae 

 (Chap. XI.), and even within these limits is very 

 imperfect. The two families appear fairly distinct, 

 as shown both by the vegetative and anatomical 

 characters and by those of the seeds. Anatomically, 

 the trend of evolution in the Lyginodendreae has 

 been towards the elaboration of the single stele, 

 in the Medulloseae (on the whole larger plants) 

 towards the breaking up of the stele. The latter was 

 an unprofitable course, ill adapted to the conditions 

 of secondary growth, and it is probable that the 

 polystelic line, after attaining an extreme elaboration, 



