170 MORPHOLOGY OF ANGIOSPERMS 



endosperm before the fertilized egg segments, as in Gonyanthes 

 Candida (Treub 7 ), HecJceria (Johnson 55 ), the Stylidaceae 

 (Burns 28 ), and Aphyllon uniflorum (Smith 46 ). Even though 

 the primary endosperm nucleus and the fertilized egg divide 

 simultaneously, the much more rapid divisions of the former 

 result in numerous free endosperm nuclei before the first few 

 segmentations of the egg have been completed. 



In the cases just cited, in which the segmentation of the 

 primary endosperm nucleus precedes that of the fertilized egg, 

 the division does not begin until after fertilization, and proba- 

 bly this is true in the majority of plants. As a consequence, 

 the impression is current that the act of fertilization is an 

 essential stimulus to the division of t the primary endosperm 

 nucleus ; and there seems to be no clear evidence to the contrary 

 when fertilization occurs, unless it be the case of Ranunculus, 

 as reported by Coulter, 20 in which free endosperm nuclei were 

 sometimes observed scattered through the embryo-sac before the 

 entrance of the pollen-tube. To this same category belong those 

 cases of habitual failure of fertilization in which endosperm 

 formation may occur, as in the Balanophoraceae, Antennaria 

 alpina ( Juel 22 ), Thalictrum purpurascens (Overton 51 ), Eicli- 

 hornia crassipes (Smith 21 ), etc. It seems to be very rare for 

 the fertilized egg to divide before the primary endosperm nu- 

 cleus, but in Naias major, in which triple fusion occurs, Guig- 

 nard 42 has observed that the fertilized egg divides immediately, 

 and has figured a two-celled embryo by the side of a primary 

 endosperm nucleus in the spirem stage. It is important to 

 note also that in this same species Guignard observed that the 

 male nucleus may fuse with the persistent synergid instead of 

 with the primary endosperm nucleus, in which case there is no 

 endosperm, but a second embryo (Fig. 103). Many cases of two 

 embryos lying side by side with an " unfertilized " primary 

 endosperm nucleus between them were observed. Recently 

 Wylie 60 has observed that in Elodea also the fertilized egg 

 divides before the primary endosperm nucleus. 



It is evident that the beginning of endosperm formation 

 does not depend absolutely upon any of the causes usually 

 assigned ; and that while it is in general approximately coinci- 

 dent with the segmentation of the fertilized egg, this is merely 

 a coincidence, for it may be independent of fertilization and 



