70 



RESEARCHES ON FUNGI 



and the columella are four parts of a single cell. Their wall is ex- 

 ceedingly thin, so thin indeed that, even in so large an illustration 

 as Fig. 28, it has to be represented by a single thin black line. The 

 wall is Uned by a layer of protoplasm which encloses a huge vacuole 

 filled with perfectly clear cell-sap. 



The protoplasm of the basal swelHng, subsporangial swelhng, 

 and columella is in general colourless and disposed in a layer 



which is no thicker than, or 

 scarcely thicker than, the cell- 

 wall against which it presses ; 

 but, around the top of the 

 subsporangial swelling (Fig. 

 28, /) and around the top of 

 the stipe where this passes into 



Fig. 28. — Pilobolus Kleinii. A median- 

 longitudinal section through the 

 upper part of a fruit-body, just 

 before the discharge of the pro- 

 jectile : a, the stipe ; 6, the subspor- 

 angial swelling ; and c, the spor- 

 angium. The sporangium is filled 

 with spores and covered with an 

 intensely black wall d which has 

 split open circumscissilely, and has 

 thus allowed a thick gelatinous inner 

 ring e, present only arovind the base 

 of the sporangium, to bulge out- 

 wards. The subsporangial swell- 

 ing, which is pyriform, has a thin 

 elastic wall lined by a layer of proto- 

 plasm which is very thin except 

 at/ where it is slightly thickened and 

 at g where it bulges inwards so as to 

 form a large biconcave septum which 

 is perforated in the centre. The 

 protoplasm at /is reddish and at g, 

 as indicated by the shading, very 

 red, especially on its upper side. The 

 subsporangial swelling is continued 

 above into a conical columella and 

 below into the cylindrical stipe. The 

 protoplasm of the stipe, swelling, 

 and columella contains one large 

 continuous vacuole h filled with clear 

 cell-sap. The broken line i passes 

 through the plane of abscission and 

 indicateswhere the Pilobolus projec- 

 tile, consisting of the sporangium 

 and columella, separates from its 

 attachment when the Pilobolus gun 

 is discharged. Magnification, 69. 



