I20 THE LIVING CYCADS 



chromosomes characteristic of the sporophyte, together 

 with the fact that nuclear divisions in immediately 

 subsequent stages of embryogeny show the anticipated 

 double number, indicates that the chromosomes con- 

 tributed by the sperm and egg are pairing. Such a 

 phenomenon has been described by Dr. A. H. Hutchinson 

 for Abies balsamea, the balsam fir. 



For a study of this phase of fertilization the cycads 

 are unfavorable, since events are very rapid, material 

 is hard to secure, and the ovules are so large that almost 

 endless time is needed for making preparations. Such 

 stages as we have secured, especially in Stangeria, con- 

 firm Dr. Hutchinson's account. 



An interesting feature common to all cycads is the 

 long interval between poUination and fertilization. 

 Fifty years ago the two phenomena were confused, or 

 rather it was not recognized that there were two phenom- 

 ena. The term fertilization was applied to pollination, 

 as in Darwin's Fertilization of Orchids by Insects, and 

 botanists were not devoting much attention to sub- 

 sequent stages. 



In Dioon edule the pollen is shed late in September or 

 early in October, and fertilization occurs late in April 

 or early in May, so that the interval between pollination 

 and fertilization is about seven months. During most 

 of this period there is a gradual growth of the pollen tube, 

 but near the close of the period there is a rapid develop- 

 ment of the sperms with their spiral, ciHated bands. 



The long interval, however, is not unique, for more 

 than a year elapses between pollination and fertilization 

 in the pines, and in the oaks the interval is still longer; 

 but in most flowering plants it is only a few days. 



