CYCADALES 



137 



cessful. In weak sugar solutions they almost explode. In a 10 per 

 cent solution, they quickly die; in a 20 per cent solution, they live a 

 little longer. 



FERTILIZATION 



Some have imagined that the archegonial chamber is a cavity in 

 which the sperms swim for a while before entering the egg. This 

 view is entirely incorrect. At the time of fertilization the pollen 

 chamber and the archegonial chamber 

 are merely moist. There is not a trace of 

 any free liquid. In studying the living 

 condition and in fixing material for de- 

 tailed study, hundreds of ovules have 

 been cut, and always there is the moist 

 membrane, but nothing more. 



A careful study of a drawing will help 

 to understand the process of fertilization 

 in a cycad (fig. 147). 



In the later stages of the development 

 of the sperms, the basal end of the pollen 

 tube becomes very much swollen and so 

 turgid that it finally bursts, discharging 

 the sperms, with liquid from the pollen 

 tube, into the archegonial chamber. This 

 liquid is the only medium in which the 

 sperms can move while in the archego- 

 nial chamber. 



As before noted, the egg becomes ex- 

 tremely turgid during the final stages 

 of its development, in fact, so turgid 

 that the contents of the egg would spurt 

 out into the archegonial chamber were it not for the turgid 

 neck cells. The liquid discharged from the pollen tube has such a 

 high pressure that sperms discharged from the pollen tube into 

 a 30 per cent solution of cane sugar move about freely. The 

 liquid from the pollen tube, coming into contact with the neck 

 cells, lowers their turgidity, and some of the contents of the upper 

 part of the egg escape into the archegonial chamber, leaving large 



Fig. 148. — Stangeria para- 

 doxa: fertilization; the sperm 

 nucleus is entering the top of 

 the egg nucleus; the ciliated 

 band is at the top of the egg; 

 X42. — After Chamberlain.'"' 



