THE EMBRYO SAC 



297 



Type 



Megasporogenesis 



Megaspore 

 mother cell 



Division 

 I 



Division 

 II 



Megagametogenesis 



Division 

 III 



Division 

 IV 



Division 

 V 



Mature 

 embrj'o sac 



Monosporic 



8 -nucleate 



Polygonum type 



Monosporic 



4 -nucleate 



Oenothera type 



Bisporic 

 8 -nucleate 

 Allium type 



Tetrasporic 



16 -nucleate 



Peperomia type 



Tetrasporic 

 16 -nucleate 

 Penaea type 



©©\ 

 f©© ®« 



Tetrasporic 

 16- nucleate 

 Drusa type 



Tetrasporic 



8 -nucleate 



FYitillaria type 



Tetrasporic 



4 - nucleate 



Plumbagella type 



Tetrasporic 



8 -nucleate 



Plumbago type 



Tetrasporic 

 8 -nucleate 

 Adoxa type 



Fig. 114. Diagram showing important types of embryo sacs in angiosperms. (From 

 MahesJiwaii.) 



region, the polar nuclei. The Oenothera type, a variation of this mono- 

 sporic type, differs from the Polygonum type in that the egg is formed 

 after the fourth, rather than the fifth, division. The mature sac has only 

 four nuclei. The antipodals and the chalazal polar nuclei are not formed. 

 These two types are monosporic. 



