THE PILOBOLUS GUN AND ITS PROJECTILE 75 



appear to him to be too large. I have estimated the number of 

 spores in a very large sporangium of P. Kleinii, which was 0- 54 mm. 

 in diameter and had been shot up to a height of 6 feet 0* 5 inch, as 

 follows. 



The sporangium was mounted in water and the cover-glass was 

 rubbed over it in such a way that the spores were arranged approxi- 

 mately in a layer two spores thick. Then the area occupied by this 



Fig. 31. — Pilobolus longipes. Two fruit-bodies from which 

 the sporangium has been pulled off under water, so as 

 to expose the columella. The columella crowns thesub- 

 sporangial swelling and has a central peak. One of the 

 black sporangia is seen to the right below. Magnifi- 

 cation, 51. 



spore-layer was measured and the upper spores occupying one-four- 

 hundredth of one square mm. were drawn and counted. With the 

 help of these data it was estimated that the sporangium had 

 contained approximately 90,000 spores. Smaller sporangia oi 

 P. Kleinii probably contain not more than half this number. In 

 P. Kleinii, therefore, the number of spores contained within the 

 sporangium varies with the size of the sporangium from about 

 30,000 to about 90,000. 



A sporangium which has dehisced and has its gelatinous ring 

 protruding around its base can be stroked away from the sporangio- 



