GINKGOALES 209 



blepharoj)last becomes bandlike, is attached to the nucleus, and 

 forms the sj)iral, cilia-bearing band of two and a half coils in connec- 

 tion with the sperms. The details of the structure and behavior of 

 the blejjtharoplast among Cycadales have been presented (p. 142), 

 and presumably they are approximately the same for the blepharo- 

 plast of Ginkgo. The mature sperms are ovoid, varying between 

 80 and no At in length, and between 50 and 85 /* in breadth, and are 

 so directed that the two adjacent sperms lie base to base (fig. 240). 



It is a little over four months from pollination to the formation of 

 sperms, the time of which varies with the latitude. For example, 

 in Tokyo sperms appear between September 7 and 22, the greatest 

 number occurring September 17 and 18; in Sendai, 200 miles farther 

 north, the optimum date is September 27; in Washington the range 

 of time is from August 25 to September 10, with September i to 3 

 as the optimum period (29). 



In 1898 several Japanese students investigated a large number 

 of sperms, correcting a few of the earlier statements and extending 

 the observations. Hirase had described a peculiar "tail," which 

 Fujii (21) and Miyake (23) showed to be an appearance that had 

 no connection with the sperm. Hirase had left the impression also 

 that the mother cells were transformed directly into sperms; but 

 Fujii and Miyake demonstrated that the sperms are formed within 

 a sperm mother cell, and they observed the cilia vibrating and the 

 sperm shifting its position within the mother cell. The sperms 

 finally break through the wall of the mother cell and escape into the 

 pollen tube, where they were observed "swimming from one end of 

 the tube to the other like a pair of large infusoria." They were 

 observed in active motion for two or three hours, the body readily 

 changing its form under pressure. Fujii (26) observed also a sperm 

 with two spiral bands, its sister sperm being normal; it is probable 

 that the blepharoplast had divided before band-formation. 



FERTILIZATION 



The swollen tip (grain end) of the pollen tube, cai)ped by the old 

 wall of the pollen grain, contains two sperms, the tube nucleus, the 

 persistent vegetative cell, and whatever may remain of the stalk 

 nucleus. At the time of fertilization, the turgid tip of the tube becomes 



