CALAMITES AND LYCOPODS 389 



OUTLINE OF LIFE HISTORY OF SELAGINELLA 



Sporophyte 



TT~ ~TT 



Microsporophyll Megasporophyll 



Microsporangium Megasporangium 



^ < Reduction > \. 

 Microspore Megaspore 



Male gametophyte Female gametophyte 

 Antheridium Archegonium 



4, 4. 



Sperm Egg 



Fertilization 



Oosperm 



4.4. 



Embryo 



4.4. 



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. 



