37 



A second hypothesis which has some evidence in its support, and 

 which should be considered in the investig-ation of the pro))leni. is the 

 possibility that the second sperm nuch^us fuses with one of the pohir 

 nuclei and that after their fusion takes place the other nucleus is 

 repelled and develops independently. This would give rise to two 

 groups of cells, as in the tirst hypothesis, one f roni the division of the 

 fecundated nucleus and containing both maternal and paternal ele- 

 ments, and the other from the division of the unfecundated polar 

 nucleus containing only maternal matter. If this process of fusion 

 and cleavage took place, the ultimate distribution of the two groups of 

 nuclei at the periphery of the em))ryo sac and the formation of islands 

 of tissue of different origin and characters would probably occur as 

 suggested in the discussion of the tirst hypothesis. 



The further investigation of the fecundation of the endosperm 

 nucleus will doubtless throw light on many questions now in doubt, 

 and the above hypotheses are suggested to direct the attention of 

 investigators to the desirability of obtaining evidence supporting or 

 contradicting them. 



Note. — Since the above bulletin went to press a second important 

 paper b3' Prof. Hugo de Vries has appeared, entitled "Sur la fecon- 

 dation hy bride de Fendosperme chez le mais" (Rev. generale de Bot, 

 Vol. 12, pp. 129-137, 15 avril, 1900). The experiments described in 

 his preliminary paper above referred to (p. 7) are described more 

 in detail and with illustrations; and the connection of double fecunda- 

 tion with the production of xenia is more fulh' discussed. No impor- 

 tant new features are given, however, which were not mentioned in 

 lis preliminary paper, so that no further discussion of the article is 

 lecessary in connection with the features brought out in this bulletin. 



a time, during which a delicate line can always be observed, indicating its origin 

 through the fusing of two nuclei. The first division is usually already beginning 

 when the pollen tube reaches the embryo sac and applies itself to the egg cell. By 

 the time fecundation is effected through the union of the sperm nucleus with the egg 

 nucleus the endosperm nucleus has already divided many times." 



