J 



1909] CHAMBERLAIN— SPERMATOGENESIS IN DIOON 233 



from left to right. In Microcycas 



Caldwell 



306 p 



direction of the other two uncertain. What 

 spiral is not known. 



Zamia has the largest sperm yet described, 

 in diameter and 222 to 332 fi in length. In Cycas the diameter is 180 

 to 210/1. In Dioon edule the living sperms measure about 230 fi 

 in diameter and 300 fi in length. In microtome sections, the sperms 

 are smaller, perhaps on account of plasmolysis, but more probably 

 because the sperms increase in size after leaving the tube. In section 

 the sperms measure about 200 p in diameter and 275 p in length. 

 Caldwell (9) gives no measurements, but, judging from his figures, 

 the sperms are comparatively small, with a diameter of about 60 fi. 



In all the cycads which have been studied, the movements of the 

 sperms are very similar, a forward movement with a rotation upon 

 the long axis. While experiments have been made, no chemotaxis 

 has yet been noted. When the sperms are mature, the neck canal cells 



are very large and turgid. 1 

 influence. 



If the foregoing account seems to consist rather largely of data, I 

 can only say that I prefer to reserve any discussion of phytogeny 

 until the investigations in which I am already engaged shall have 

 been completed. 



The sporophylls of the staminate cone are rather large, and bear 

 about 250 sporangia, a larger number than in any cycads except 

 Cycas, Encephalartos, and Macrozamia. The output of spores per 

 sporangium is about 30,000, a larger output than in Zamia, Cera- 

 tozamia, or Encephalartos, the onlv genera in which this feature has 

 been noted. 



may 



SUMMARY 



chromosomes 



<—«« *put so early that the number may appear largei. 



There is only one prothallial cell and that is persistent, lne 

 report of an evanescent prothallial cell in Zamia is probably due to a 



1 ^1 T\f'£%"r*w»i j. • 



^interpretation 



radiat 



ions 



very 

 ytopl 



The 



