toro) CHAMBERLAIN—DIOON EDULE 417 
into a sugar solution, the nucleus often slips out from the cytoplas- 
mic sheath, and the cytoplasm then rinses off from the spiral band, 
leaving the band with its cilia almost free from any cytoplasm. 
Before the pollen tubes have begun to discharge, the megaspore 
membrane over the archegonia has been ruptured, so that there is 
no obstruction between the sperms and the necks of the archegonia. 
What causes the sperm to enter the egg? The classical experi- 
ments on chemotaxis would suggest a solution, but there is no 
free open passage as in bryophytes and pteridophytes, in which the 
small sperms may move freely in response to a slight stimulus. 
On the contrary the neck is closed, and the sperm becomes greatly 
constricted while entering, so that, whatever the force may be, it 
Is a very strong one. Against the theory that chemotaxis is 
responsible for the movement, it must also be remembered that so 
skilful an investigator as Miyake (5) was unable to detect any 
chemotactic response when studying the sperms of Cycas revoluta, 
although he used the solutions which are uniformly effective with 
the sperms of pteridophytes, and in addition used the squeezed- 
out contents of the Cycas eggs. 
It is well known that in many algae a small portion of the con- 
tents of the egg is extruded just before fertilization, a passage to 
the egg being facilitated in this way. In Dioon, just before fertili- 
zation, numerous preparations show a little protoplasm about the 
necks of the archegonia, and for a long time I assumed that it had 
been squeezed out from the egg by the pressure of the knife as the 
square block containing the archegonia was being cut out from the 
top of the endosperm before fixing. It was also noted that when 
material near the fertilization period is dropped into water or the 
fixing agent, a small bubble appears at the neck of the archegonium. 
_ The drop of liquid from the pollen tube has a very high osmotic 
pressure, and when it comes into contact with the extremely turgid 
neck cells, these lose so much of their contents that, in preparations, 
they appear more or less plasmolyzed. The pressure within the 
egg has been increasing until the contents are retained only by 
_ the rigidity of the turgid neck cells, and consequently even a slight 
decrease in turgidity of the neck cells would allow the escape of a 
_ Small portion of the cytoplasm of the upper part of the egg, together, 
