FCRrffER STUDIES O.V G YAfXOSPF.F AfS. 



3'3 



only microsporangia. These leaves, while they resemble the ordinary leaves, 

 are smaller and correspond to the stamens. Upon 

 the under side, as shown in fig. 369, the microspo- 

 rangia are borne in groups of three or four, and these 

 contain the microspores, or pollen grains. The ar- 

 rangement of these microsporangia on the under side 

 of the cycas leaves bears a strong resemblance to the "^ 

 arrangement of the sporangia on the under side of 

 the leaves of some ferns. 



631. The ging'ko tree is 

 another very interesting plant 

 belonging to this same group. 

 Tt 1? a relic of a genus which 



thick 

 stem, fem-like 

 leaves, and 

 cone of male 



flowers. 



flourished in the remote 

 past, and it is interesting 

 also because of the re- 

 semblance of the leaves 

 to some of the ferns like 

 adiantum. which sug- 

 gests that this form of 

 the leaf in gingko has 

 been inherited from some 

 fern-like ancestor. 



632. While the resem- 

 blance of the leaves of 

 someofthegymnosperms 

 to those of the ferns sug- 

 gests fern-like ancestors 

 for the members of this 

 group, there is stronger 

 evidence of such ances- 

 try in the fact that a pro- 

 thallium can well be de- 

 termined in the ovules. 

 The endosperm with its 



ormed archegunia is t(j be considered a prothallium. 

 Spermatozoids in some gymnosperms. — But witliiu the past two 



it has been discovered ingingku. cycas, andzamia, all belonging to this 



Two 



Fifi. 371- 

 spermatozoids in end of pollen tube of cycas, 

 drawing by Hirase and Ikeno.) 



well-f< 

 633 



year; 



(After 



