THE PILOBOLUS GUN AND ITS PROJECTILE 155 



and to the resistance consequently offered to the j)assage of the 

 sporangia by surface tension. 



A number of sporangia were floating at the surface of some water 

 contained in a crystallising dish. With a pipette some of the water 

 and some of the sporangia were removed from the dish, and a drop 

 of the water bearing a sporangium was caused to hang at the end 

 of the pipette, as shown in Fig. 76, A. The sporangium remained 

 at the surface of the hanging drop in an inverted position, with 



Fig. H\.- Piloboluv loiKjipes. Diagrams sliowing sporangia in water. The 

 vvettable annular naass of jelly of each sporangium is immer.sed in 

 tlio surface film of water, while the black vmwettable sporangial 

 wall protrudes into the air. A, a sporangium attached to a drop of 

 water hanging from a pipette. B, a test-tube partly filled with water, 

 and C another test-tube overfilled with water. Some sporangia have 

 been placed in the water film. As indicated by the arrows, the 

 sporangia in B move toward the centre of the surface film of water, 

 while those in C move toward the edge. If the black sporangial 

 wall were wettable instead of unwettable, the movements would be 

 in directions opposite to those indicated. Somewhat enlarged. 



its gelatinous side submerged in the surface film of water and its 

 unwettable black convex side protruding into the air. 



As is well known, glass is wettable by water and, when water 

 is set in a glass dish, the water film bends upwards against the glass. 

 If now tiny wettable objects which float, such as hollow glass beads, 

 are set in a small glass vessel containing water, they move to the 

 sides ; whereas, if similar objects but unwettable, such as hollow 

 glass beads coated with paraffin wax, are set in the water, they move 

 away from the sides of the vessel toward the middle of the film of 

 water. ^ Some sporangia of Pilobolus were placed in water contained 



1 C. V. Boys, Soap Bubbles and the Forces which Mould them, The Romance 

 of Science Series, S.P.C.K., London, 1895, pp. 33-34. 



