FATE OF SECOND MALE NUCLEUS IN EMBRYO-SAC. 1^9 



shows certain well-marked characters of the male parent, and accord- 

 ing to the hypothesis of Webber, De Vries, and others, these hybrid 

 characters are transmitted by the male nucleus. In some cases the 

 endosperm does not reveal hybrid characters, but only those of the 

 mother plant, and Webber explains the fact by assuming that in those 

 cases the endosperm nucleus may not have been fecundated. As an 

 explanation of another peculiar feature of xenia in certain varieties of 

 maize, which is shown by a variegated or mosaic endosperm, Webber 

 suggests that probably the second male nucleus may not have united 

 with the endosperm nucleus, but it may have been able to divide in- 

 dependently. If this should occur, there would then be formed in the 

 embryo-sac nuclei of two distinct characters, one group from the 

 division of the endosperm nucleus and one from the sperm nucleus. 

 Or a second hypothesis lies in the probability that the second male 

 nucleus fuses with one of the polar nuclei, and that after fusion the 

 other polar nucleus is repelled and develops independently. In view 

 of the fact that in the sea-urchin (Boveri, '95) the male nucleus is 

 capable of independent division under certain circumstances, these 

 hypotheses are certainly very suggestive, but they have, as yet, among 

 plants no support based upon observation, especially since partheno- 

 genesis is unknown in maize. Before these suggestions can be of 

 much value in explaining the phenomenon, it is necessary to know 

 whether a male nucleus is of itself capable of division in the embryo- 

 sac, and whether one of the polar nuclei without having united with 

 the other or with a sperm nucleus is also capable of independent 

 division. 



Although the union of a male nucleus with the endosperm nucleus 

 may be conclusively shown to be the cause of hybrid endosperm in maize, 

 yet that fact alone is not sufficient to justify the unqualified conclusion 

 that the fusion represents a real fecundation. Strasburger, in discus- 

 sing this question at some length in the Botanische Zeitung (pp. 293- 

 316, 1900), argues forcibly against the doctrine of a double sexual 

 process as understood by Nawaschin, and proposes a different interpre- 

 tation of the two sets of nuclear fusions. For the union of the male 

 nucleus and that of the egg-cell which results in an individual sporophy te, 

 the expression generative fecundation is used, while the fusion of the 

 other male nucleus with the endosperm nucleus is designated vegetative 

 fecundation. In the interpretation of Strasburger, the need of genera- 

 tive fecundation by means of sexual nuclei of different origin lies in the 

 equalization of individual variations, which is necessary for the continu- 

 ance of the species, while in vegetative fecundation there is merely the 



