33 



The fact that the embryo itself may be ohano-ed in color bv cross ; 

 fertilization, as observed b}- Gaertner, Laxton, Darwin. Giltay, and 

 others, favors the conclusion that the color in the endosperm of corn 

 may be due to the fecundation of the embryo sac nucleus. If the 

 embrj^o, the immediate result of the union of the male and female 

 pronuclei, can show the effect of changed color in the seed, it favors 

 the interpretation that the endosperm, the immediate result of the 

 union of the endosperm nucleus with one of the male nuclei, would 

 probably be able to show similar changes of color. 



In the writer's experiments all kernels showing xenia, which have 

 been grown, have proved to be true hybrids, and there can be l)ut 

 little doubt that this is usually if not always the case. Correns makes 

 the definite statement that "the plant growing from a kernel showing" 

 xenia is always a h3'brid." In races which show xenia on crossing 

 the change may be used as a hand}- index to demonstrate that a cer- 

 tain kernel has been hybridized and is thus a convenient check in 

 practical hybridization work. The converse of this proposition, how- 

 ever, that all seeds which have been hybridized show xenia, is not 

 true, even in cases where xenia conmionly occurs. In quite a number 

 of instances of crosses of different races which commonly show xenia, 

 no evidence of the cross was visible, the kernels remaining the same 

 as those of the mother parent. This was very noticeably the case in 

 experiments la, lb, and Ic, where some of the kernels showed xenia, 

 but where fifty-one which showed no indication of xenia proved to be 

 undoubted hybrids. It would »eem probable that in these cases the 

 embryo sac nucleus was not fecundated, but developed without fecun- 

 dation taking place. So little is known about double fecundation that, 

 while it seems undoubtedly to occur in some plants, we do not know 

 whether it is a process necessary to development. While the egg cell, 

 which is the important organ, must in almost all cases be fecundated, 

 a few truly parthenogenetic cases are known where the egg cell develops 

 without fecundation having taken place. It would thus not be sur- 

 prising if the embryo sac nucleus should be capable of functioning 

 even if it were not fertilized. The evidence from the non-appearance 

 of xenia in so many instances of true hybrids of varieties where xenia 

 may occur favors this interpretation. 



The peculiar feature of xenia showing in spots on the kernels, as in 

 Hickory King X Cuzco (experiment la, PI. I, figs. 9-12), and occasion- 

 ally on one-half of a kernel, as in Pedrick's Perfected Golden Beauty 

 X Cuzco (experiment 20a, PL I, fig. 24), and Gilman Flint X Sto well's 

 Evergreen (p. 29), is interesting in this connection. A hypothesis 

 has occurred to the writer which may explain such phenomena, but 

 the evidence in its favor is yet very incomplete. As stated above, in 

 very many cases of true hybrids of parents capable of showing xenia 

 25258— No. 22 3 



