142 MORPHOLOGY OF GYMNOSPERMS 



their agency. Until insect pollination is proved, it is safer to assume 

 that the pollen is carried by the wind, as is generally supposed. 



Whether in artificial culture or in the pollen chamber, the pollen 

 tube begins to grow at once, but in cultures the growth is very limited, 

 neither Juranyi (5) nor Strasburger (7) having been able to get 

 the division of the generative cell. Under natural conditions the 

 development continues without interruption from pollination to fer- 

 tilization, a period of about four months in Cycas revoluta, about 

 five months in Zamia floridana, and about six months in Dioon edule. 

 The pollen grain end is pushed into the open cavity of the pollen 

 chamber, while the haustorial end penetrates the nucellus, branching 

 occasionally and running so near the surface that the brown lines due 

 to the tubes are easily visible to the naked eye. Starch is abundant 

 in the pollen grain and during all stages in the development of the 

 pollen tube. 



The generative cell soon divides, forming two cells which have 

 been called the stalk and body cells on account of their usual relations 

 to each other in most gymnosperms. In Ikeno's figures of Cycas 

 revoluta (27) these two cells lie side by side, and it would seem that 

 either might function further; while in Zamia, Dioon, Microcycas, 

 and Ceratozamia they have the more usual fore and aft position 

 (fig. 159). The stalk cell does not divide again, but increases greatly 

 in size and becomes filled with large starch grains; and since it has 

 been found to be sterile in all gymnosperms, it may be regarded as 

 representing the actual stalk cell of an antheridium. In that case, 

 the body cell is the real primary spermatogenous cell. The body 

 cell increases both in size and cytoplasmic content, but contains little 

 or no starch. As these two cells enlarge, the prothallial cell behaves 

 in a peculiar way, pushing into the stalk cell until it often presses 

 against the wall between the stalk and body cells (figs. 158, 159). 



The most interesting feature in the development of the male game- 

 tophyte is the fact that motile sperms are produced. The cilia by 

 which the sperms swim are the culmination of the development of 

 a small body called the blepharoplast, which appears in the body cell 

 several months before the latter divides. When first unmistakably 

 distinguishable, there are two blepharoplasts, one at each pole of the 

 nucleus of the body cell, but occasionally they may be nearer together 



