154 



RESEARCHES ON FUNGI 



that the surface of the black sporangial wall shines with a white 

 light owing to its being covered by a thin film of air.^ 



A wide test-tube was almost filled with water and then covered 



with a dung-ball which bore a number 

 of Pilobolus fruit-bodies in such a way 

 that the fruit-bodies pointed directly 

 downwards to the water. After a time, 

 a number of the fruit-bodies discharged 

 their sporangia which were shot down- 

 wards at the surface of the water 

 which was only one centimetre or so 

 distant (c/. Fig. 75 in which the water 

 is 3 cm. from the sporangia). The 

 velocity of the sporangia was probably 

 not less than 10-20 feet per second. 

 Most of the sporangia were shot through 

 the surface film of the water, descended 

 through the water for a short distance, 

 and then slowly rose until they again 

 reached the surface film under which 

 they remained without breaking through 

 into the air. However, some of the 

 sporangia, when shot downwards, failed 

 to penetrate through the surface film of 

 water. This failure was evidently due 

 to the sporangium- wall being unwettable 



Fig. 75. — The discharge of Pilobolus projectiles 

 into water. A wide test-tube was half filled 

 with water. A piece of horse dung bearing 

 fruit-bodies of Pilobolus longipes was then re- 

 moved from a culture dish and placed in the 

 mouth of the tube so that the sporangia 

 looked downwards. When the sporangia 

 were shot away, many of them failed to 

 penetrate the surface film of the water, owing 

 to the sporangial wall being unwettable. 

 Natural size. 



1 A submerged sporangium may sink to the bottom of the water or slowly rise 

 and come to the surface, where it may either break through the surface film and 

 resume its old position with its black wall protruding clear above the water or it 

 may fail to break through the surface film and lie just beneath it. 



