242 SHEPHERD'S PURSE. 



fertilization 19 has taken place a membrane is devel- 

 oped about the oosphere, making it a sexual spore. 



By divisions 20 in one plane the oospore at once 

 extends toward the interior of the ovule as a chain of 

 cells, the suspensor or pro-embryo, the basal cell of 

 which becomes large and bladder-like. The apical cell 

 at the free end of the suspensor, by repeated division 

 in several planes, forms a cell mass, which presently 

 assumes the form of the embryo. 81 The ovule after 

 various changes of minor importance in this connec- 

 tion becomes at last a ripe seed. 



19 For an account of the nuclei of the pollen spore and oosphere, and 

 their union in the fertilizing act, see Strasburger, Neue Untersuchungen. 



20 For methods of cell division in the developing embryo of Cap- 

 sella (with figures) see Bessey, Bot. , p. 424 ; Westermaier, Die ersten 

 Zelltheilungen im Embryo von Capsella, Flora, 1876, p. 483. 



21 For further description of the development of the embryo see Gray, 

 Struct. Bot., p. 283 ; Prantl and Vines, Text-book, p. 204 ; Bessey, Bot., 

 p. 423 ; Sachs, Text-book, 2nd Eng. ed., p. 585. 



