384 



THE SPERMATOPHYTES 



The other sperm nu- 

 cleus is known in a 

 number of forms to pass 

 to the center of the sac 

 and unite with the two 

 polar nuclei, constitut- 

 ing a triple fusion (Fig. 

 307, p, p, ss), and form- 

 ing a large nucleus, 

 called the endosperm 

 nucleus. Since the en- 

 dosperm nucleus has 

 an important history in 

 the development of the 

 seed, this peculiar behav- 

 ior of the second sperm 

 nucleus is important, and 

 it is called the double 

 fertilization of the em- 

 bryo sac. 1 



1 Double fertilization is 

 probably tha explanation of 

 the phenomenon called xenia, 

 which is the appearance at 

 once in the seed of some 

 character of the male parent. 

 Thus a yellow or white kind 

 of corn, when pollinated from 

 a blue or red variety, will 

 produce blue or red kernels. 



This color in the corn is pres- 

 The first sperm nucleus /s fusing with the egg ent in the endosperm , and 



FIG. 307. Fertilization in the embryo sac 

 of the lily 



nucleus e ; the second sperm nucleus ss is fusing 



the character comes into the 



with the two polar nuclei p near the center of 



the sac, constituting the so-called double ferti- seed through the second 



lization ; p, pollen tube ; *, synergid breaking sperm nucleus. For an ac- 



down; ant, antipodals; ii, inner integument; count of xenia see Webber, 



m, micropyle "Xenia, or the Immediate 



Effect of Pollen in Maize, v United States Department of Agriculture, 



Division of Vegetable Physiology and Pathology, Bulletin 22, 1900. 



