CHAPTER XII 

 PARTHENOGENESIS AND VEGETATIVE APOGAMY 



Parthenogenesis and vegetative apogamy are very 

 important to keep in mind in connection with work in 

 genetics. Geneticists have paid too little attention to 

 these phenomena, and as a consequence their data are 

 not always reliable. The distinction between the two 

 terms is as follows. Parthenogenesis is the develop- 

 ment of an embryo by an unfertilized egg, while vege- 

 tative apogamy is the development of an embryo by 

 another cell of the female gametophyte. The term 

 "apogamy" includes both, meaning the production of a 

 sporophyte by a gametophyte without involving an 

 act of fertilization. Parthenogenesis is not peculiar to 

 any region of the plant kingdom, and a few illustrations 

 will be sufficient. 



In water molds (Saprolegnia) parthenogenesis is very 

 common. All stages in the abortion of the male organ 

 (antheridium) are found and still eggs apparently 

 germinate as freely as if fertilized. In fact, in many 

 species of Saprolegnia it is a question whether fertiliza- 

 tion ever occurs. 



Ferns are notably apogamous, any cell of the game- 

 tophyte (including unfertilized eggs) producing an 

 embryo under certain conditions. This miscellaneous 

 production of embryos by the gametophyte is an 

 impressive illustration of the fact that any vigorous 

 protoplast, under appropriate conditions, can produce 



"5 



