FERTILIZATION 159 



lower polar nucleus enters the combination, as was also observed 

 by Shibata 54 in Monotropa uniflora] but in Lilium it has been 

 observed that if the lower polar nucleus happens to be the more 

 favorably placed the male nucleus fuses with it first. In Ascle- 

 pias Cornuti (Erye 60 ) both male nuclei are vermiform and 

 more or less curved, and one of them was observed in contact 

 with a polar nucleus near the antipodal cells, the micropylar 

 polar nucleus being some distance away and nearer the egg- 

 apparatus. That the male nucleus may thus traverse much of 

 the embryo-sac is also shown in Nigella damascena and Anem- 

 one nemorosa, in both of which Guignard 53 observed the male 

 nucleus uniting with the fusion nucleus near the prominent 

 antipodal cells. 



At present there is a decided tendency among botanists and 

 zoologists to distinguish two distinct phenomena in fertiliza- 

 tion namely, the stimulus to growth and the mingling of ances- 

 tral qualities. Strasburger 43 regards the latter process as the 

 essential one, and the stimulus to growth as only providing the 

 conditions which make it possible to obtain the advantages 

 resulting from a mingling of ancestral plasma masses. In a 

 later paper 59 he makes the statement that fluctuating variations 

 do not furnish a starting-point for the formation of new species, 

 but that it is the principal function of fertilization, through 

 the mingling of ancestral plasma masses, to keep the species 

 characters constant. The essence of fertilization lies in the 

 union of organized elements. It was to insure this essentially 

 generative fertilization that, in the course of phylogenetic devel- 

 opment, the inability of the sexual cells to develop independ- 

 ently became more and more marked. The term generative 

 fertilization is used in contrast w T ith vegetative fertilization, 

 which is merely a stimulus to growth. Hence Strasburger re- 

 gards the fusion of the male nucleus with the polar nuclei as 

 merely vegetative fertilization, and lacking the essential feature 

 of a sexual fusion. It is worthy of note that Ernst 61 finds in 

 Paris quadrifolia and Trillium grandiflorum a striking differ- 

 ence between generative and vegetative fertilization, the fusion 

 of the male nucleus with the egg-nucleus being complete, so 

 that a typical resting nucleus is formed ; while the polar nuclei 

 begin to form spirems even before the male nucleus arrives, and 

 in the group of three nuclei the two polar nuclei and the male 



