144 Outline of Genetics 



the endosperm tissue is sister to the embryo sporophyte. 

 In other words, in angiosperms the endosperm and 

 embryo are twins. This means that the endosperm of 

 angiosperms belongs to the sporophyte generation, 

 although of course it is a distinct individual which pro- 

 duces no progeny. The embryo sporophyte is a parasite 

 upon its twin and devours it. 



It will be recognized that there is some reason for 

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

 claims, that is, of distinguishing between sporophyte 

 and gametophyte tissue ? The cytological distinction, 

 based on chromosome count, is that the sporophyte is 

 2X tissue and the gametophyte is x tissue. Applying this 

 test, it is found that endosperm tissue is neither x nor 

 2X, but 30;, as might be expected from the triple fusion. 

 The conclusion involves several possibilities, as follows: 

 30: is evidently nearer 2X than x, and therefore endosperm 

 tissue is more like sporophyte 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 is female gametophyte. On the basis of 

 predominance, therefore, endosperm tissue is more like 

 female gametophyte tissue than anything else. Finally, 

 there is a third alternative, and that is that the 30; con- 

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

 which would mean that endosperm is neither gameto- 

 phyte nor sporophyte. 



These are the claims and the evidence as to the 

 angiosperm endosperm. Opinion is not settled, but the 

 facts are clear. This prepares for a consideration of 

 the bearing of this situation upon genetics. The geneti- 

 cist is not much concerned about the exact morphologi- 



