4IO STRUCTURE AND LIFE HISTORIES 



in frequently not having the embryo develop until after 

 the seed is planted, and in not having the embryo undergo 

 a period of rest between its formation and its final develop- 

 ment into a mature sporophy te ; the absence of an embryo 

 characterizes some of the fossil relatives of Cycas, 



The genus Cycas is the only living genus of plants which 

 produces seeds w^ithout developing either a cone or a flower, 

 but produces the seeds on sporophy Us borne on I he main 

 stern. It is the simplest of all living seed-plants, to this 

 extent, being in this respect as lowly organized as the 

 ferns. 



OUTLINE OF LIFE HISTORY OF A CYCAD 



The Cycad plant 

 (Sporophyte) 



Microsporophylls Megasporophylls 



>l^ >!' ■A' -^ 



Microsporangia Megasporangia (ovules) 



4, ^ — Reduction — > \. 



Microspores Megaspores 



4, 4. 



Male gametophyte Female gamctophyte 



(Pollen-grain) (Endosperm) 



i i 



Vestigial antheridium Archegonium 



Generative cell 



4. 



Sperms Egg 



Fcrtilizahuii 



Oosperm 



a 



Embryo 



New Cycad plant 

 (Sporophyte) 



;on 



1 



