The Endosperm in Inheritance 147 



sperm nucleus is comparable with the zygote, and the 

 endosperm tissue is sister to the embryo sporophyte. 

 In other words, in angiosperms, embryo and endosperm 

 are twins. This means that the endosperm of angio- 

 sperms belongs to the sporophyte generation, although 

 of course it is a distinct individual which produces no 

 progeny. The embryo sporophyte is a parasite upon its 

 twin and destroys it. 



It will be recognized that there is some reason for 

 each of these claims. Is there any way of testing the 

 claims, that is, of distinguishing between sporophyte and 

 gametophyte tissue ? The cytological distinction is that 

 the sporophyte is 2X tissue and the gametophyte x 

 tissue. Applying this test it is found that endosperm 

 tissue is neither x nor 2X, but 2,x, as might be expected 

 from the triple fusion. The conclusion involves several 

 possibihties, as follows : 3^1; is evidently nearer 2X than x, 

 and therefore endosperm tissue is more like sporophyte 

 tissue than gametophyte tissue; but on the other hand 

 two of the x's have come from the female gametophyte, 

 and therefore two-thirds of the endosperm nucleus is 

 female gametophyte tissue. On the basis of predomi- 

 nance, therefore, endosperm tissue is more like female 

 gametophyte tissue than anything else. Finally, there 

 is a third alternative, and that is that the 3a; condition 

 deserves to be set apart in a category by itself, which 

 would mean that the endosperm is neither gametophyte 

 nor sporophyte. 



These are the claims and the evidence as to the na- 

 ture of angiosperm endosperm. Opinion is not settled, 

 but the facts are clear. This prepares for a consid- 

 eration of the bearing of this situation upon genetics. 



