390 



MORPHOLOGY OF GYMNOSPERMS 



After reaching the deep pollen chamber, the exine of the spore is 

 sloughed off and the intine with its contents is completely freed. The 

 two prothallial cells soon disappear, and the nucleus of the body 

 cell divides to form two equal male nuclei. The tube nucleus moves 

 around the cavity of the grain and comes to rest against the wall, 

 and soon after the pollen tube is put out from this point of contact 



439 



440 



44-1 



Figs. 436-441. — Ephedra trif urea: germination of the microspore; ^, first prothal- 

 lial cell; pr^ and />r^ first and second prothaUial cells; ai, nucleus of antheridium 

 initial; tn, tube nucleus; g, generative cell; bii. nucleus of body cell; stn, nucleus of 

 stalk cell; X 1,500.— .\fter Land (18). 



(figs. 442, 443). As previously stated, the greater number of pollen 

 grains rest upon the necks of the archegonia, and fertilization is pos- 

 sible within ten hours, as shown by experiment. The tube forces 

 its way between the neck cells, rarely destroying them in its passage. 

 In Ephedra distachya (22) the two male nuclei lying in the general 

 cytoplasm of the body cell are said to be unequal. The equality or 

 inequality of such cells should be based upon an estimate of their 



