CALAMITES AND LYCOPODS 389 



OUTLINE OF LIFE HISTORY OF SELAGINELLA 



Sporophyte 



Microsporophyll Megasporophyll 



Microsporangium Megasporangium 



4, < — Reduction — > J, 



Microspore Megaspore 



I i 



Male gametophyte Female gametophyte 



i I 



Antheridium Archegonium 



i i 



Sperm Egg 



Oosperm 



a 



Embryo 



a 



Mature sporophyte 



350. Marks of Progress. — With the introduction of 

 heterospory we recognize a distinctly new feature of the 

 sporophyte generation. Structural differentiations asso- 

 ciated with difference in sex have hitherto been confined 

 to the gametophytic generation, but now such distinctions 

 appear for the first time in the sporophyte. This is a 

 long step forward, and marks Selaginella as a more highly 

 organized form than the lycopods, horsetails, and ferns. 

 Other marks of progress are : 



1. The reduction of the vegetative tissue of the 

 gametophytes (to only one cell in the case of the male" 

 gametophyte). 



2. The entire dependence of the gametophytes upon the 

 sporophytes for nutrition. 



3. The retention of the female gametophyte, through- 

 out its entire existence, almost entirely within the wall 

 of the megaspore. 



