THE ENDOSPERM 181 



these racial characters is due to the incompleteness of the trip 

 fusion, since it is well known that division of the primary e^\u- 

 sperni nucleus often begins before the constituent nuclei nave 

 lost their identity. In fact, Webber calls attention to the begin- 

 ning of division before complete fusion in the case of the eggs 

 of certain animals, and the same is true of the sexual fusion- 

 nucleus of some Gymnosperms. An alternative hypothesis sug- 

 gested by Webber is that the male nucleus may fuse with one of 

 the polar nuclei, the other remaining independent and dividing. 

 These hypotheses are valuable in suggesting investigation as to 

 whether the male nucleus ever divides independently in the em- 

 bryo-sac, or whether it may unite with one polar nucleus, the 

 other dividing independently. 



It remains to consider the morphological character of the 

 endosperm of Angiosperms. In view of the details as to its 

 origin and behavior given above, it is evident that it is a struc- 

 ture peculiarly difficult to interpret. The view has long been 

 held, dating from Hofmeister, that the endosperm is belated 

 vegetative tissue of the female gametophyte, stimulated in a 

 general way to develop by the act of fertilization, and in every 

 way the morphological equivalent of the structure bearing the 

 same name among Gymnosperms. Strasburger 37 has suggested 

 that this postponement of the formation of endosperm is of 

 advantage in avoiding the waste that would follow its formation 

 and separation from the parent plant with every unfertilized 

 ovule. Of course the serious difficulty in this view of the nature 

 of the endosperm was that it offered no historical explanation 

 of the fusion of the polar nuclei. It could only claim that 

 fusions of vegetative nuclei, evidently resulting in growth- 

 stimulus, are by no means unknown., and in fact occur in the 

 endosperm itself. This view does not appear to have been 

 seriouslv disturbed by the claim of Le Monnier 9 in 1887, that 

 the fusion of the polar nuclei is a sexual process, and that there- 

 fore the endosperm is a second embryo modified to serve as 

 food tissue. 



With the discovery of the fact that, at least in many cases, 

 a male nucleus enters into the organization of the primary endo- 

 sperm nucleus', the old view has been seriously menaced. The 

 commonly used phrases "double fertilization" and "double 

 fecundation ' ; indicate general consent to the view that this 



