FERTILIZATION 



189 



absorbers against its impact, does not rest on a sound basis (see 

 also Dahlgren, 1938). In Zauschneria latifolia (Johansen, 19316) 

 pollen tubes were found to enter even those ovules whose embryo 

 sacs had degenerated and virtually disappeared. 



Detailed information regarding the exact manner of discharge of 

 the male gametes is lacking. In Crepis capillaris (Gerassimova, 

 1933) and Taraxacum kok-saghys (Warmke, 1943) the tip of the 



ABC 



Fig. 112. Stages in fertilization in Petunia; globular bodies scattered inside embryo 

 sac are starch grains. A, mature embryo sac surrounded by cells of integumentary 

 tapetum. B, upper portion of embryo sac at time of double fertilization; note two 

 branches of pollen tube, through which two male gametes have been discharged; 

 just behind bifurcation are two X-bodies. C, upper portion of embryo sac, showing 

 zygote and two endosperm nuclei with cell plate forming between them; X-bodies 

 are still visible inside tip of pollen tube. (After Cooper, 1946.) 



pollen tube becomes "wedged in" between the egg and the polar 

 fusion nucleus, so that both the male gametes are discharged in close 

 proximity to their mates. Fagerlind (1939) noted some embryo 

 sacs of Peperomia in which the tip of the tube had divided into two 

 short branches, one of which was directed toward the egg. Cooper 

 (1940, 1941, 1946) refers to a similar bifurcation of the tip of the 

 pollen tube in Portulaca, Phryma, and Petunia (Fig. 112), one 

 branch becoming closely appressed to the egg and the other extend- 

 ing in the direction of the polar nuclei, and suggests that the two 

 male gametes reach their destinations by way of these separate 



