232 



MORPHOLOGY. 



size of the female nucleus before the fusion of the two takes place. 

 In figs. 306 and 307 are shown the entering pollen tube with 

 the sperm nucleus, and the fusion of the male and female nuclei. 

 457. Fertilization in plants is fundamentally the same as 

 in animals. In all the great groups of plants as represented by 

 spirogyra, cedogonium, vaucheria, peronospora, ferns, gymno- 



Fig. 304. 



Two- and four-celled stage of embryo-sac of lilium. The middle one shows division of 

 nuclei to form the four-celled stage. (Easter lily.) 



sperms, and in the angiosperms, fertilization, as we have seen, 

 consists in the fusion of a male nucleus with a female nucleus. 

 Fertilization, then, in plants is identical with that which takes 

 place in animals. 



458. Embryo. After fertilization the egg develops into a 

 short row of cells, the suspensor of the embryo. At the free end 

 the embyro develops. In figs. 309 and 310 is a young embryo 

 of trillium. 



459. Endosperm, the mature female prothallium. During 

 the development of the embryo the endosperm nucleus divides 



