PILOBOLUS UMBONATUS 



175 



The sporangium-wall is intensely black except below, where it is 

 very pale-grey or colourless. After a sporangium has dehisced and 

 just before it is discharged, one can observe the colourless lower 

 part or fringe of the -sporangium-wall overlying the protruding jelly. 



The ratio of the width of the sporangium to the width of the 

 subsporangial swelling in Pilobolus umbonatus is almost exactly |, 

 whereas this ratio in P. 

 longipes is about f and in 

 P. Kleinii about f. When 

 one looks at a living fruit- 

 body of P. umbonatus in 

 side view with a hand-lens, 

 one perceives at a glance 

 that the width of the 

 sporangium relatively to 

 the width of the subspor- 

 angial swelling is much less 

 in this species than in P. 

 longipes and P. Kleinii. 

 An apical view of a fruit- 

 body showing both sporan- 

 gium and subsporangial 

 swelling is reproduced in 

 Fig. 105, F (p. 210). 



A sporangium, after 

 being discharged, dries 

 and shrinks and becomes 



acutely pointed (Fig. 105, K). When sporangia of P. umbonatus, 

 P. longipes, and P. Kleinii have been discharged on to the side of 

 a glass dish and lie mixed near the top and one examines them in 

 lateral view with a hand-lens, one can readily distinguish those of 

 P. umbonatus from the two other species by the fact that the former 

 are conical in shape, whereas the latter are rounded. 



When a sporangium which has just been discharged on to a glass 

 sHde and has dried (Fig. 87) is examined from above with the 

 microscope, it can be seen : (1) that the main convex portion of the 

 sporangium-wall, which covers the spores, is intensely black and is 



Fig. 



87. — Pilobolus umbonatus. Photomicro- 

 graph of the upper side of a dried discliarged 

 sporangium on a glass sHde. No. 1, tlie dried 

 cell-sap ; No. 2, the broad fiat clear ring- 

 layer of jelly : No. 3, the narrow transparent 

 fringe of the sporangium -wall overlying the 

 jelly ; and No. 4, the convex very black 

 main portion of the sporangium -wall cover- 

 ing the spores. Magnification, 120. 



