CYTOLOGY OF REFRODUCTION IN ANGIOSFERMS 



139 



ovary are one or more ovules. Each ovule consists of a central portion, 

 the nucellus, surrounded by one or two integuments with an opening, the 

 micropyle. In the nucellus a subepidermal cell, either at once or after 



Fig. 102. — Typical ovule.s, niega.sporogenesis, and female gametophyte development in 

 angiospeims. 1-10 from lettuce; 11-15 from bloodroot. 1-6, development of megaspore 

 quartet from mega.sporocyte in ovule. 7-15, development of female gametophyte from one 

 surviving megaspore of quartet, a, antipodal cells; e, egg; i, integument; m, micropyle; 7i, 

 nucellus; p, polar nuclei; s, synergids. {From preparations by J. Einset.) 



division, enlarges and differentiates as a megasporocyte (Fig. 102). This 

 cell divides into a quartet of megaspores, each wdth the reduced chromo- 

 some number. Often the outer cell of the two present after division / 

 does not divide again, so that the quartet is incomplete. One of the 



