198 INTRODUCTION TO EMBRYOLOGY OF ANGIOSPERMS 



male gametes move in the forward direction only. This would 

 hardly be possible unless the male gametes have the power to move 

 independently of the strands of cytoplasm. 



Concerning the actual course of fusion of the gametic nuclei, only 

 a few observers have described it in sufficient detail. The most 

 careful account is that of Gerassimova (1933) on Crepis capillaris. 

 At the time of its approach to the egg nucleus, the male nucleus has 

 the appearance of a continuous thread rolled into a ball (Fig. 114A), 

 which soon begins to unwind and spread out with its entire surface 

 adjacent to the nuclear membrane of the egg (Fig. 114B). It then 

 gradually "immerses" itself within the egg nucleus, although still 

 remaining distinguishable for a long time (Fig. 114C-F). Mean- 

 while, a nucleolus arises from it "at first as a small, scarcely visible, 

 weakly stained drop, which gradually increases in size" (Fig. 

 114E, F). At the same time the body of the sperm "becomes more 

 porous and breaks up lengthwise, losing its continuity" (Fig. 114G- 

 H). Very soon the male chromatin becomes indistinguishable from 

 the female, and it is only the presence of the two nucleoli which 

 serves to distinguish the fertilized from the unfertilized egg (Fig. 

 114I-K). Finally, however, the male nucleolus increases in size 

 and fuses with the female nucleolus "thus closing the perceivable 

 phenomena of sexual union of the nuclei" (Fig. 114L). 



The fusion of the second sperm with the secondary nucleus takes 

 place in very much the same way. Here also the sperm has the 

 shape of a rolled thread, which gradually unwinds itself and comes 

 in contact with the secondary nucleus all along its surface. This is 

 followed by the immersion of the sperm into the secondary nucleus 

 and the formation of a small nucleolus. Finally the two chromatins 

 merge into each other, followed by a fusion of the nucleoli. 



From the less frequent occurrence of stages in the fertilization of 

 the secondary nucleus, Gerassimova concludes that triple fusion is 

 accomplished more quickly than syngamy. She states that in 

 triple fusion "the formation of the nucleolus takes place so rapidly 

 that it is almost impossible to catch the beginning of the process" 

 and that "although fertilization always begins first in the nucleus 

 of the egg-cell, the stage of a complete fusion of the nuclei is often 

 simultaneous and sometimes terminates even earlier in the nucleus 

 of the endosperm." In several of her preparations she found that 

 triple fusion had already ended (as judged by the fusion of the 



