180 ANGIOSPERMS. 



manifestation of a growth stimulus. Vegetative fecundation according 

 to this interpretation finds its parallel in such phenomena as described by 

 Klebs ('98, 1900), Loeb ('99, '01) and Nathansohn (1900), in which, 

 by means of physical or chemical stimuli, such as increased tempera- 

 ture or an increase of the osmotic power of the surrounding fluid, 

 unfecundated egg-cells have been made to develop parthenogenetically 

 through certain embryonic stages. According to the view of Stras- 

 burger, therefore, sexual reproduction embraces fundamentally two 

 great and far-reaching factors, namely, the union of hereditary ele- 

 ments and the imparting of a growth stimulus. In the fusion of a 

 male nucleus with the endosperm nucleus, only one of these factors, 

 the stimulus to growth, is manifested, since the interrupted growth of 

 the endosperm is enabled to continue. The result is the same whether 

 the second sperm nucleus unites with the endosperm nucleus or not, 

 and furthermore because the endosperm is not an individual in the 

 sense that the embryo sporophyte is an individual. It is further true 

 that the endosperm nucleus may divide and give rise to several nuclei 

 before the contents of the pollen tube are discharged into the embryo- 

 sac, and in case that no pollen tube reaches the embryo-sac, these same 

 endosperm nuclei never continue their development. It is reasonable 

 to conclude, therefore, that a growth stimulus may be imparted to 

 the endosperm by the act of fecundation in the egg-cell, just as the 

 vegetative tissue of certain parts of the pistil are stimulated to growth 

 by the presence of the pollen tube. 



Many who agree with Strasburger may probably not consider it 

 necessary or advisable to use the term " vegetative fecundation." The 

 author does not see the necessity of associating the idea of fecundation 

 with this process of nuclear fusion, for the reason that nuclear fusions 

 in vegetative cells do not signify an act of fecundation. In the light 

 of all the known facts, it seems that we have to do here with purely 

 vegetative fusions, and that we are not justified in attributing to such 

 nuclear fusions the idea of sexuality. Although the upper polar 

 nucleus is the sister of the egg-nucleus, it does not necessarily follow 

 that the former is also a female nucleus, since it is certainly not true that 

 the sister cells of egg-cells are even potential gametes. If such an 

 assumption were accepted, then the ventral canal-cell of the arche- 

 goniates might be considered an egg-cell, a doctrine to which the 

 author can not, as yet, subscribe. 



