CYCADALES 



131 



fusing into a band, is drawn out into a spiral with several turns 

 (fig. 141). From this spiral band, lying just beneath the Hautschicht, 

 thousands of cilia are developed. They pierce the Hautschicht and 

 extend into the cell cavity. The topography of the nucellus with its 

 pollen tubes during these stages is shown in figs. 142 and 143. 



In all of the cycads, except Microcycas, there are two sperms in 

 each pollen tube. In Microcycas, according to Caldwell, ^^ there 



Fig. 140. — Stangeria paradoxa: the body cell has divided to form two sperms, and 

 each blepharoplast has broken into numerous granules which will form the spiral band. 

 The nuclei of the sperms are still comparatively small (January 11, 1913). X400. 



are usually 16 sperms. Dr. Dorothy Downie found 8 to 11 body 

 cells, so that the number of sperms would range from 16 to 22. 



Spermatogenesis in Microcycas was studied in great detail by Dr. 

 DowNEE'" and the results not only show how the large number of 

 sperms originates, but suggest what is probably the real nature of the 

 generative cell and stalk cell (figs. 144 and 145). After the prothallial 

 cell has been formed, the next mitosis gives rise to a tube cell and a 

 generative cell. The latter divides in the usual way, forming a stalk 

 cell and a body cell; but from this point, the behavior is peculiar to 

 Microcycas. The stalk cell divides, giving rise to another body cell, 



