TJie Eiidosper))! in TjiJicrUance 151 



cytological peculiarity, is really significant in inherit- 

 ance. 



The foregoing case, which is the only endosperm 

 character that is inherited in this peculiar way, provides 

 a conspicuous criticism of the presence and absence 

 hypothesis (see also pp. 51, 112). Whichever of the two 

 characters be assumed to be due to the presence of 

 a gene, a demonstration is provided to the effect that 

 two absences will dominate one presence. In spite 

 of this outstanding exception, the terminology of the 

 presence and absence hypothesis is retained by practi- 

 cally all geneticists, and is, in fact, employed even in 

 connection wath the case of corneous and floury endo- 

 sperm. 



Webber (8), in 1900, experimenting on xenia in corn, uncov- 

 ered some interesting anomalies. Pollen from a red-grained race, 

 applied to silks of a white-grained race, should result in solid red 

 grains if xenia is normal. Of course Webber actually obtained 

 this result in the vast majority of cases, but occasionally there 

 appeared two other types of grains : (a) white grains covered with 

 numerous, irregular patches of red, commonly called ''mottled"; 

 {b) grains of which a large and uninterrupted area of the aleurone 

 was pure white, while the remaining area of the aleurone was just 

 as pure red, commonly called "mosaic." For these cases he con- 

 structed an ingenious explanation. 



Normally, the second male nucleus fuses with the fusion 

 nucleus, and the result is a solid red grain. In some cases, how- 

 ever, the second male nucleus (i) does not join with the other two; 

 while in still other cases the second male nucleus (2) fuses with but 

 one of the polar nuclei, leaving the other polar nucleus to act 

 independently. Either of these irregularities, Webber felt, would 

 serve to account for the anomalous grains, for in either case female 

 nuclei would be left to act independently in the formation of part 

 of the endosperm. That part of the endosperm would neces- 

 sarily show colorless aleurone, since the female parent to the cross 



