GENERAL RESULTS— PTEROPSIDA 647 



These stems have taken an aberrant line of develop- 

 ment, through the elaboration of anomalous secondary 

 growth, and thus present some analogies with the more 

 modified of the recent Cycadaceous stems. They may 

 well have been Cycadophyta, though probably not 

 closely allied to the known Mesozoic or recent types. 



The relation of the Pteridosperms to the Cycado- 

 phyta is as clear as that to the Ferns, and indeed, as 

 we have seen, it is often difficult to draw the line 

 between the two first-named classes. For the present, 

 it is convenient to keep the Pteridosperms distinct, on 

 account of their relatively primitive character, but there 

 is every reason to hope that further discoveries will 

 effectually link them on to the typically Gymno- 

 spermous Cycadophyta. The anatomical resemblances, 

 which led to the recognition of the Cycadofilices as a 

 transitional group, have been immensely strengthened 

 by the discovery of the seeds, which are sufficient in 

 themselves to demonstrate a near affinity between the 

 Pteridosperms and the Cycads. Curiously enough, the 

 relation is closest with the seeds of the recent Cyca- 

 daceae, a group of which the geological history is still 

 obscure. Those of the Mesozoic Bennettiteae are not 

 so readily comparable, and evidently represent a more 

 advanced stage of evolution, their seeds having been 

 modified and in some respects simplified in correlation 

 with the development of the complex fruit. 



As regards the microsporangiate organs of the 

 Pteridosperms, our present somewhat scanty informa- 

 tion indicates that they were of the nature of synangia 

 (p. 399) ; they thus find a remarkable analogy in the 

 compound pollen -sacs of the Mesozoic Bennettiteae 



