118 THE EVOLUTION OF PLANTS 



to a younger and more progressive branch, 

 which has succeeded to the inheritance of the 

 old stock. 



Our attempts to picture to ourselves the march 

 of evolution are necessarily very imperfect 

 we can only trace the successive scenes in the 

 broadest outline. 



In the history of the evolution of the Seed- 

 plants there are two evident gaps. (1) We do 

 not know how the transition from the Pterido- 

 sperms to the Cycadophytes was effected. The 

 gap between a Pteridosperm and such a Cycad 

 as the female plant of Cycas, is not, it is true, 

 a very wide one, and we know that the Cycas 

 type was of great antiquity, going back to the 

 earlier Mesozoic. But though we may well 

 compare the seed-bearing frond of a Pterido- 

 sperm with the leaf-like carpel of Cycas, while 

 the seeds themselves offer no difficulties, yet, 

 when we come to the male plant, there are al- 

 ready considerable differences, for we know of 

 nothing in Pteridosperms, with their unspecial- 

 ised, stem-borne sporophylls, at all like the Cyca- 

 daceous cone. Still less have we anything to 

 show how the complex flower of the Bennettitese 

 arose among the flowerless Pteridosperms. The 

 stamens, indeed, with their frond-like form and 

 numerous compound pollen-sacs are altogether 

 Pteridospermous, not to say Fern-like, but the 



