BASIDIA AND THE DISCHARGE OF SPORES 23 



exists as that to which reference has just been made. Using a 

 fruit-body of Coprinus sterquilinus, I tried the effect of breaking 

 off spores from their sterigmata at a stage when the spores had 

 attained full size but were only half -ripened. The protoplasm was 

 still flowing into the spores, for the basidia had become only about 

 half-emptied. I found that a half-ripened spore, isolated from its 

 sterigma in the manner indicated, remained quite turgid although 

 the canal leading into it through its membrane at the hilum was 

 still open so far as the cell- wall was concerned. Plasmolysis could 

 be effected readily with a solution of 10 per cent, potassium nitrate. 

 These observations seem to show that the canal has so small a 

 diameter that the osmotic pressure of the cell-sap is insufficient 

 to press the protoplasmic contents of the spore through it. It is 

 also very probable that, when a spore is removed from a sterigma, 

 the opened sterigmatic canal is too narrow to permit of the osmotic 

 pressure of the basidium driving the basidial contents out through 

 it. We may therefore draw the conclusion that a double wall 

 is unnecessary to close the ends of a spore and its sterigma at 

 the moment of spore-discharge ; for, even if they remain open, the 

 cell-contents cannot be forced out through them. 



Assuming tentatively that no double membrane is formed 

 between a ripe spore and its sterigma, and that, when a spore is 

 discharged, the end of the sterigma is simply broken across, what 

 can be the nature of the force which causes spore-projection ? 

 As yet I can give no satisfactory answer to this question. The 

 remarks which follow are intended to stimulate further investiga- 

 tion which may lead to a solution of the problem. Before assuming 

 the presence of a double membrane between spore and sterigma 

 at the moment of discharge, we ought to try to solve the problem 

 by taking into account all the following facts : 



(1) The existence of a structure called the hilum a tiny blunt 

 process projecting from the base of the spore. This is always 

 developed and is the point where a spore separates from the sterigma. 

 It is therefore probably the seat of the force which brings about 

 discharge. 



(2) The extreme narrowness of the necks of all sterigmata. The 



