1907] LAND— EPHEDRA TRIFURCA 275 



after being placed In the sugar solution^ the fluted exine is ruptured 

 by a longitudinal split extending along one side of the grain from end 

 to end, and the intine with its contents is completely freed. The two 

 prothallial cells soon disappear and the cytoplasm of the prothallial 

 end becomes very vacuolate. The body cell next divides, the spindle 

 being parallel with the long axis of the pollen grain {fig. i). At the 

 same time the tube nucleus and the stalk cell, which lie at opposite 



mov 



side, or occasionally they may lie as shown in fig. 2. The tube nucleus 

 comes to rest against the wall, assumes a lenticular shape, and soon 



afterward the poll 



Appear- 



ances seem to indicate that the pollen tube is produced at the point 

 of separation of the tetrads, but this could not be definitely determined 

 because of the symmetry of the pollen grain and the possibility of a 



mass 



The male nuclei are of equal volume and are truly elliptical. One of 

 them almost invariably passes in advance of the stalk cellj which takes 

 a position in advance of the rearmost male nucleus (fig-j)- Measure- 

 ments of male nuclei show them to be exactly of like dimensions; 

 neither is there any optical difference. Their relative position in the 

 pollen tube is the only evidence^ if evidence it be, of any inequahty. 

 There is little doubt that the male nucleus nearest the end of the tube 

 will succeed in fusing wuth the egg nucleus because of its favorable 

 position. Within ten hours from the time the pollen grains were 

 placed in the sugar solution the pollen tubes were sufficiently long to 

 reach the egg. After twenty-four hours the tubes ceased to elongate, 

 at which time they were three to four times longer than is neces- 

 sary to penetrate to the egg. The stalk nucleus is usually about half 



the diameter of the male nucleus. The tube nucleus is variable in 



common 



As has been shown in the study of spermatogenesis and oogenesis, 

 the pollen grains come to rest on the bottom of the pollen chamber 

 in contact with the gametophyte, in the vicinity of or on the necks of 

 the archegonia. Occasionally pollen grains rest on the sides of the 

 pollen chamber as well as on the bottom, but by far the greater number 

 rest on the bottom, and in consequence the pollen tubes are put out 

 directly into the archegonia. Since all material studied was fixed 



