384 



THE SPERM ATOPHYTES 



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 the 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 nrst sperm nucleus fa fusing with the egg . . ,, endosi)erm and 

 nucleus e ; the second sperm nucleus ss is fusing ^ospei m, am 



with the two polar nuclei p near the center of the character comes into the 

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

 lization ; p, pollen tube ; s, 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," United States Department of Agriculture, 

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



FIG. 307. Fertilization in the embryo sac 

 of the lily 



