196 INTRODUCTION TO EMBRYOLOGY OF ANGIOSPERMS 



Persidsky (1926) states that in Orobanche cumana the sperm nucleus 

 fertilizing the egg is shaped like a hemisphere and is larger than the 

 other, which has an oval outline. In 0. ramosa (Finn and Rudenko, 

 1930) also, the sperm nucleus fusing with the egg is looser and more 



F. 



i 



Fig. 113. Fertilization in Vallisneria americana. A-D, portions of pollen tubes 

 from stylar region, showing male cells; note also vegetative nucleus in A, B, and D. 

 E,F, elongated male cells from pollen tubes which have entered the ovarian cham- 

 ber. G, upper part of embryo sac, showing egg, one synergid, two male cells, and a 

 densely staining mass formed by tube and second synergid. H, first male nucleus 

 lying tangent to the egg nucleus within the egg cell; nucleus of second male cell 

 emerging from its sheath. /, nucleus of first sperm fusing with egg nucleus and 

 second sperm nucleus touching the upper polar. Note the two X-bodies at the 

 tip of the pollen tube. J, later stage, showing male and female nuclei in advanced 

 stage of fusion, and second sperm nucleus in contact with secondary nucleus. {After 

 Wylie, 1923,1941.) 



