180 MORPHOLOGY OF ANGIOSPERMS 



as first pointed out by Kornicke, 3 and this has been most clearly 

 established in the crossing of races of corn. It also appears 

 that this influence of foreign pollen extends only to the color 

 of the endosperm and the chemical composition of the reserve 

 materials, the size and form of the kernels remaining un- 

 changed, as stated by Correns. 25 For example, if white or yel- 

 low corn be crossed with pollen from a red corn, many of the 

 resulting kernels will lie red or variously mottled ; or if sweet 

 corn, with its wrinkled and sugary endosperm, be crossed with 

 pollen from dent or flint corn, the result is smooth kernels with 

 starchy endosperm. 



The possibility of such a direct effect of pollen was for a 

 long time questioned, and the phenomenon remained inexpli- 

 cable. With the discovery of "double fertilization" or triple 

 fusion by Nawaschin 23 in 1808, the explanation of xenia oc- 

 curred simultaneously and independently to Correns, 21 ' De 

 Vries, 27 and Webber, 40 the paper of the last investigator being 

 a very complete resume and discussion of the subject based upon 

 his own extensive experimental work. To claim that the phe- 

 nomenon of xenia, as observed in corn, is due to the fusion of 

 one of the male nuclei with the primary endosperm nucleus was 

 an assumption, although an irresistible one, until such fusion 

 was demonstrated by Guignard 41 in 1001. It has been proved 

 repeatedly that when xenia occurs the embryo is a hybrid, so 

 that we have in xenia not only a hybrid endosperm, but a gross 

 demonstration of the occurrence and effect of the triple fusion, 

 and also an indication of the sort of characters that can be 

 brought into a structure by a male nucleus. 



In many cases of xenia following the crossing of races of 

 different colors, the kernels are not of uniform color, but are 

 parti-colored or variously mottled. The ingenious explanation 

 suggested by Webber is that the male nucleus has failed to unite 

 with the fusion-nucleus and may be able to divide independ- 

 ently. If so, there would result two cell-races of different 

 characters that might lie variously arranged with reference to 

 one another in the endosperm. Tt is entirely conceivable that 

 under favorable conditions of nutrition and physical environ- 

 ment an independent male nucleus may begin divisions, espe- 

 cially as this has been observed in the case id' certain animal- ; 

 but it seems more probable that the independent appearance of 



