THE EMBRYO 



269 



sequence of events from the time of pollination to the first division 

 of the zygote. These data are given in the accompanying table. 

 In some plants the first division of the zygote and that of the 

 primary endosperm nucleus occur at approximately the same time. 

 As examples may be cited Alisma, Damasonium (Dahlgren, 1928), 



Hordeum distichon palmella 



Cuscuta (Smith, 1934), Echinodorus (Dahlgren, 1934) and Taraxacum 

 kok-saghys (Cooper and Brink, 1949). Less frequently the zygote 

 may divide before the primary endosperm nucleus as in Cynomorium 

 (Steindl, 1945), Restio (Borwein et ah, 1949), and some species of 

 Allium (Weber, 1929). In any case eventually the development of 

 the endosperm proceeds at a quicker rate and surpasses that of the 

 embryo. 2 



2 Oxybaphus nyctagineus (Cooper, 1949) is an exception to this. At first nuclear 

 divisions in the endosperm keep pace with cell divisions in the embryo, but after 



