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586 THE AMERICAN NATURALIST. [VoL. XXXIX. 
surface a texture smooth or wrinkled, is stored within the endo- 
sperm. ; 
The clearness of xenia in the maize has led to a number of 
careful studies on cross-pollination beginning with the work of 
Vilmorin (1866), Hildebrand (1867), and Friedrich Körnicke 
(1872). The possible explanation of xenia in maize through 
“double fertilization " which introduces qualities of the male 
parent from the pollen into the endosperm was suggested by 
experiments of De Vries on hybridizing maize in the summers 
of 1898-99 and Correns and Webber in 1899. De Vries ('99, 
: 00) pollinated a wrinkled-seeded sugar corn from a variety of 
smooth starchy corn and obtained smooth starchy kernels which 
when cultivated in the succeeding summer were found to be true 
hybrids. He concluded that this furnished experimental proof 
that the endosperm of the sugar corn was affected by the 
entrance of a sperm nucleus from the starchy variety according 
to the theory of “double fertilization " proposed by Nawaschin 
(98) 
Correns ('99b) in the same year expressed similar conclusions 
in a clear statement of the theoretical aspects of the problem of 
venia as found in Zea mays. Correns advanced a number of 
propositions some of which should be noted for their speculative 
interest. Thus he states (proposition 7) that the influence of 
the new pollen (Z. e., from the male parent of the hybrid) is 
expressed as xenia only in the endosperm and (proposition 8) 
only in the pigment present or the chemical nature of the reserve 
material whether starchy or sugary. If the two races differ 
only in the presence of one character, as in the color of the 
aleurone layer, that character is only found in xenia when 
brought by the pollen (proposition 10). Xenia is then only 
expressed in a hybrid (proposition 14) by the formation of a pig- 
ment which the race of the female parent does not possess or of 
a more complicated chemical compound (such as starch) in place 
of a simpler (as dextrin). Correns (: O1) later presented in a 
lengthy paper, beautifully illustrated, the full results of his 
studies on xenia in maize with a discussion of the hybrids. 
Webber (: 00) also simultaneously with De Vries and Correns 
Conducted extensive experiments in hybridizing a number of 
