THE PILOBOLUS GUN AND ITS PROJECTILE 147 



and are allowed to dry up in a watch-glass, a moderately heavy 

 white deposit is left behind. This deposit, when seen with the 

 microscope, is found to consist of a fine flocculent precipitate through 

 which run numerous, long, fairly thick, branched needles. A 

 similar deposit forms the halo around a discharged sporangium 

 (Figs. 71, 72, and 73). It is, of course, the substances dissolved in 





Fiu. 72. — Filohulwi lomjipes. Sporangia whicli were shot vertically up- 

 wards for a distance of 4 feet 7 inches on to the under surface of a 

 horizontal glass plate. Each sporangium is surrounded by a halo made 

 up of a precipitate of salts, etc., which were dissolved in the large 

 drop of cell-sap which accompanied the sporangium in its flight. 

 Photographed dry in transmitted light. Natural size. 



the cell-sap which enable the sap to exercise its osmotic (turgor) 

 pressure. 



Since the discharge of the projectile is in large measure due to the 

 osmotic (turgor) pressure of the cell-sap, and since this pressure is 

 due to the sap's content of dissolved substances, it is of interest to 

 determine what these substances are. 



Employing the slide-crusher method already described, and 

 working on four cultures of Pilobolus longlpes which came to maxi- 

 mum fruition on four different mornings, I succeeded in harvesting 



