CHAPTEK IX 



THE EMBRYO 



IT is perhaps impossible at present to formulate any defi- 

 nite laws for the development of the embryo of Angiosperms. 

 The details recorded are very nu- 

 merous and confusing, the great- 

 est amount of variation occurring 

 in allied forms and even in the 

 same species. Undue attention 

 probably has been given to the 

 succession of cell divisions in the 

 earliest stages of the embryo, for it 

 is at this very period that the em- 

 bryo seems to be peculiarly respon- 

 sive to the conditions that surround 

 it. What the conditions are that 

 determine that a cell-wall in a 

 given stage of the embryo shall 

 run now in one plane, now in an- 

 other, or even shall fail to develop, 

 are unknown ; but the study of a 

 large series of embryos makes it 

 evident that if there is a normal 

 sequence of cell divisions it is 

 being constantly interfered with. 



It is probable that when these FIG- Bl. Cqpsella Bursa - pastori*. 



minor variations are neglected, cer- 

 tain laws of general development 

 will appear that are concerned with 

 the organization of the great body regions rather than with the 

 succession of cell divisions (Fig. 81). 



187 



Photomicrograph of seed showing 

 embryo, endosperm, and develop- 

 ing testa ; x 125. 



