LIFE HISTORIES OF ALG^E 24I 



OUTLINE OF LIFE HISTORY OF ASCOPHYLLUM 



Spermagonial-plant Oogonial-plant 



(Sporophyte) (Sporophyte) 



Spermagonium Oogoniun 



(Sporangium) (Sporangium) 



Protoplast of spermagonium Protoplast of oogonium 



(spore-mother-cell) (spore-mother-cell) 



4- >l< 4^ 4^ Reduction '^ ^ ^ ^ 



Spore Spore Spore Spore Spore Spore Spore Spore 



64 sperms 8 less 4 eggs 



(Reduced male gametophyte) (Reduced female gametophyte) 



Oosperms (rest) 



Spermagonial-plants Oogonial-plants 

 (Sporophytes) (Sporophytes) 



226. The Cause of Sex. — One of the many very inter- 

 esting things revealed by a study of the life history of 

 Ascophyllum nodosum is the fact that part of the fertilized 

 eggs give rise to plants that bear only male gametes, and 

 the remainder to plants that bear only female gametes. 

 Since the fundamentally different individuals develop 

 under identically the same environmental influences, we 

 are forced to the inference that the difference lies in the 

 fertilized eggs themselves. Some of them appear to be 

 male-producing, others female-producing. In what does 

 this fundamental difference consist? Here is a very 

 important problem, but further consideration of it must 

 be postponed until Chapter XXII. 



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