The Endosperm in InJicritance 143 



vegetative body of the female gametophyte, and this tis- 

 sue is called the endosperm. In angiospcrms, however, 

 a new situation introduces doubt. It can be said as before 

 that after the germination of the megaspore everything 

 within the megaspore wall is female gametophyte tissue, 

 but it cannot be said that fertilization affects the egg only, 

 for one of the sperms fuses as regularly with the fusion nu- 

 cleus as does the other sperm with the egg. It will be re- 

 membered that the fusion nucleus is formed by two nuclei, 

 which have migrated from each end of the sac, so that 

 when the sperm enters into the fusion there is a triple 

 fusion. After fertilization the fertilized egg, of course, 

 forms the ombryo sporophyte, but usually every nucleus 

 of the old gametophyte disappears except the fertilized 

 fusion nucleus, which then forms the endosperm in which 

 the young sporophyte is imbedded. For this reason the 

 fertilized fusion nucleus is usually called the endosperm 

 nucleus. 



A comparison of the angiosperm and gymnosperm 

 seeds reveals the following contrast (fig, 23). In the 

 appearance of their essential structures, they are exactly 

 alike, and on that basis some might claim that the endo- 

 sperm of angiosperms is the same as that of gymnosperms, 

 that is, gametophyte tissue. The opposing claim is that, 

 although the gymnosperm endosperm is gametophyte 

 tissue, the situation in angiosperms is essentially dif- 

 ferent. In angiosperms, the endosperm docs not arise 

 from morphologically unmodified gameto})hyte tissue, 

 as in gymnosperms, but entirely from the en(losj)erm 

 nucleus, and this nucleus is clearly the product of fusion 

 of male and female nuclei. With such an origin, the 

 endosperm nucleus is comparable with the zygote, and 



