SPERMATOPHYTES 



145 



with the egg, and that the other sperm simply wasted away, 

 accomplishing nothing. Now it is known that while one 

 sperm unites with the egg, the result being a fertilized egg, 

 the other sperm unites with the endosperm nucleus, which 

 then represents a case of triple fusion. This phenomenon of 

 fertilization in the angiosperm embryo-sac has been called 



" double fertilization." The fer- 

 tilized egg forms the embryo 

 (the young sporophyte), and the 

 fertilized endosperm nucleus 

 forms the endosperm, a tissue 

 that feeds the embryo. 



FIG. 116. A, embryo of 

 a Dicotyledon, show- 

 ing the terminal stem 

 tip between the two 

 cotyledons (which 

 therefore arise from 

 the side of the em- 

 bryo) ; B, an embryo 

 of a Monocotyledon, 

 showing the terminal 

 cotyledon, and the 

 stem tip arising on one 

 side ; in both cases 

 the hypocotyl is the 

 other (lower) end of 

 the embryo. 



FIG. 117. Seed of violet, the left figure 

 showing the hard seed coat, and the right 

 figure the abundant endosperm that sur- 

 rounds the embryo ; observe the regions 

 of the embryo, namely, hypocotyl, two 

 cotyledons, and a minute plumule (to form 

 the stem with its leaves) between the 

 bases of the cotyledons. After BAILLON. 



This double fertilization accounts for some things in con- 

 nection with seeds that were not understood before. It 

 means that the pollen parent can transmit its characters not 

 only to the embryo, but also to the endosperm. For example, 

 if corn with red ears be used as the pollen parent, and corn 

 with white ears as the egg-producing parent, it would be 

 natural to expect a mixture of white and red in the ears of 

 the plant produced by the embryo. But the fact had long 



