SPORE EXPULSION AMONG PHYCOMYCETES 



183 



upper portion persists as a convex cap over the sporangium; the 

 lower portion remains attached to the base of the sporangium 

 with the jelly-like mass formed around the fissure. The sporan- 

 gium is now ready for discharge, and this phenomenon occurs as 

 soon as the swelling of the subsporangium reaches the limits of 

 extensibility. Since the papil- 

 lar area constitutes the weak- 

 est portion of the wall, the 

 subsporangium opens at this 

 point, squirts away about 

 one-half the fluid content of 

 the subsporangium and stipe, 

 and carries along the sporan- 

 gium with the jet of sap. The 

 gelatinous mass present around 

 the base of the sporangium 

 before discharge is carried 

 along with the sporangium 

 and sticks it to vegetation. 

 When the plants are eaten, 

 the spores pass through the 

 alimentary tract and are 

 evacuated, undigested and 

 unharmed. 



The initial velocity of the 

 sporangia of P. longipes and 

 P. kleini approximates 20 ft. 

 per second. Buller's observa- 



Fig. 29. Stages in discharge of spo- 

 rangia bv Pilobolus. A. Mature spo^ 

 rangium atop the subsporangial swell- 

 ing. B. Circumscissile rupture of outer 

 membrane of sporangium and lique- 

 faction around base of sporangium. 

 C. Collapsed subsporangium after 

 discharge. (After Buller.) 



tions showed that the ex- 

 plosive force is sufficient to carry sporangia to a vertical height 

 of 72.5 in. and a horizontal distance of 91.5 in. in P. longipes 

 and 90.5 in. in P. kleini. When he prepared a special drum with 

 tissue paper as the membrane forming its head, the impingement 

 of sporangia was audible at a distance of 21 ft. Moreover the 

 sporangia are discharged with sufficient force to be felt when 

 they strike the face. 



Nearly everyone has observed that flies may become attached 

 to windows in attics and other little-used rooms. Upon closer 

 observation a whitish halo may be noted to surround such flies. 

 This halo, 2 or 3 cm in diameter, is produced by discharged 



