SPERMATOl'HYTA 



397 



Apomixis. Irregularities in the normal process of sexual reproduction 

 occur occasionally in some angiosperms, constantly in others. Apomixis 

 is a condition in which sexual reproduction in the flower is replaced by 

 some form of asexual reproduction. It may take the form of partheno- 



FiG. 338. Successive stages in early development of the embryo of Sagittaria variabilis, a 

 monocotyledon. A and B, three-celled proembryos, showing synergid {syn), basal cell 

 (a), middle cell (b), and terminal cell (c) from which the cotyledon is derived; C, division 

 of middle cell into two cells, one of which (s) gives rise to the stem tip; D, slightly older 

 stage; E, formation of four cells from the terminal cell; F, further development of the 

 middle region; G, differentiation of dermatogen in the terminal region; H, further develop- 

 ment of dermatogen and differentiation of middle region into hypocotyl (h) and stem tip 

 (s); 7, later stage. {After Schaffner.) 



genesis, which is the development of an embryo from an unfertilized egg. 

 This has been observed in a number of angiosperms, such as Thalictrum, 

 Antennaria, Alchemilla, Erigeron, and Taraxacum. In all these and sim- 

 ilar cases the reduction of chromosomes fails to take place in connection 



