DEVELOPMENT OF THE EMBRYO AND ENDOSPERM 385 



m 



363. The development of the embryo and endosperm. The 



fertilized egg develops the em- 

 bryo, but as in gymnosperms, 

 there is generally a preliminary 

 growth called the suspensor 

 (Fig. 309, D, E, If, s), which car- 

 ries the young embryo into the 

 center of the sac. The endo- 

 sperm nucleus begins to divide 

 at once after its formation, by 

 the triple fusion of the second 

 sperm nucleus with the two po- 

 lar nuclei (Fig. 307). It gives 

 rise to a large number of nuclei, 

 which become distributed in the 

 protoplasm of the rapidly enlar- 

 ging embryo sac (Figs. 308, e ; 

 309, H, e). Later, walls begin to 

 form around these endosperm 

 nuclei, first in the outer regions 

 of the embryo sac, and finally 

 the whole sac becomes filled 

 with a delicate tissue. 



This tissue is called the endo- 

 sperm, and the embryo becomes 

 imbedded within it as in the pine. 

 But this endosperm has, of course, 



a very different origin from that 



, .. , . FIG. 308. Development of the embryo 



of the gymnosperms, and is a and the endosperm of the lily 

 special development peculiar to 



r * The embryo em has developed from 



the angiosperms. The group of 

 antipodal cells possibly corre- 

 sponds to the endosperm in the 

 gymnosperms, and the egg ap- 

 paratus has been regarded as a 



the fertilized egg; e, endosperm 

 nuclei which have been derived from 

 the triple-fusion nucleus, that is, 

 the two polar nuclei united with the 

 second sperm nucleus (compare with 

 Fig. 307) ; ii, inner integument ; m, 

 micropyle 



