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 Kornicke 

 (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, 

 : oo) 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 

 xenia 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 (i. 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 (: 01) 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 (:oo) also simultaneously with De Vries and Correns 

 conducted extensive experiments in hybridizing a number of 



