348 BOTANICAL GAZETTE [October 



monosporangiate sporophytes, determines the development 

 much wider range of structures than the aDDrooriate sex orsra 



Parthenogenesis 



A strict application of the term parthenogenesis to the germina- 

 tion of an unfertilized egg is intended here. The facts that have 

 accumulated in reference to parthenogenesis among plants seem to 

 justify the following conclusions: 



An egg may function as a spore in that it may germinate with- 

 out fertilization. It seems evident, however, that an egg so differs 

 from a spore in constitution that it needs a different kind of stimulus 

 for germination. Usually this stimulus is applied in connection 

 with the act of fertilization, but it may be applied in some 

 other way. 



The peculiar organization of the egg for fertilization is deter- 

 mined at the reduction division. If the reduction division does not 

 occur, parthenogenesis is more likely to occur, and the egg is prob- 

 ably incapable of fertilization. 



If spores are eliminated from the life history, as in animals 

 and some plants, reduction occurs in connection with gamete- 

 formation. 



An egg necessarily produces a sporophyte, and a spore a game- 

 tophyte, but vegetative protoplasts of either generation may be 

 organized to produce either generation; that is, they may function 

 as eggs or spores, dependent upon the determiners they have 

 received. 



In general, therefore, parthenogenesis differs from reproduction 

 by other protoplasts only in requiring a more specific stimulus, 

 a fact which ordinarily prevents eggs from germinating unless 



fertilized. 



Some conclusions concerning sexuality 



Any general survey of the facts connected with sexual repro- 



them to be very numerous 



apparently contradictory, but they are all consistent with some 

 general situation that determines sexuality. A review of the 

 more prominent facts referred to in the preceding pages ma 



,- sug- 



.•* 



