THE PILOBOLUS GUN AND ITS PROJECTILE 83 



columella becoming more or less drawn together or becoming 

 polygonal (Fig. 35), while the compression from above downwards 

 causes the more or less swollen conical wall of the columella to 

 flatten and to come directly into contact with the surface of the 

 substratum. The columella-wall, when dry, adheres to the sub- 

 stratum (Fig. 41, c), and thus to some extent assists the gelatinous 

 ring in attaching the sporangium to a grass-leaf or other object. 



Fig. 39. — Pilobolus Klein ii. Discharged sporangia, from a pure culture, attached 

 to a sheet of glass, photographed by reflected light. To show the characteristic 

 rounded depressions (dimples) which were developed in the sporangium -wall 

 as the sporangia dried up. Magnification, 60. 



The sporangium as a whole, as it dries after discharge, contracts 

 considerably, perhaps to one-quarter of its original volume. This 

 contraction is due in part to the shrinkage and disappearance of the 

 large central columella cavity, as already described, and in part to 

 the loss of water from the spores and from the substance lying 

 between them. Loss of water from the interior of the sporangium 

 results in : (1) a flattening of a lower zone of the originally convex 

 part of the sporangium-wall, so that this zone becomes added to 

 the fringe {vide Figs. 33 and 34, between Nos. 3 and 4, and Fig. 41, 



