152 RESEARCHES ON FUNGI 



away from the under surface of the cover-glass. The sporangia 

 in due course were discharged. Although their initial velocity must 

 have been 10-20 feet per second ^ and they must have struck the 

 cover-glass within less than one five-hundredth of a second after 

 leaving their sporangiophores, yet, when they landed on the cover- 

 glass, they settled there with their gelatinous lower surfaces turned 

 upwards and in contact with the under surface of the glass (c/. 

 Fig. 74, B). The results of this experiment and of others ^ made 

 when determining the vertical range of the Pilobolus gun prove that, 

 whatever may be the speed at which it is travelling, a sporangium 

 normally lands on any object it may strike so that its basal gelatinous 

 surface is next to the surface of the object. 



An attempt to explain why a sporangium lands'with its gelatinous 

 side toward the surface of the object struck was made by Grove ^ 

 who says : " The upper surface of the sporangium is round and 

 practically smooth (though not actually so), and the lower edge and 

 face are occupied by the gelatinous substance. Now, when a 

 sporange is thrown upwards it will certainly rotate as it flies ; if 

 the smooth top only comes in contact with the glass (or other vertical 

 surface) it will not adhere, and the sporange will fall down again. 

 But, if any portion of the gelatinous substance touches the glass, 

 the force of progressive attraction between it and the thin film of 

 moisture which will usually cover the glass * must invariably bring 

 the lower, somewhat plane, surface of the sporangium in close 

 contact with the glass. In the case of the paper, the sporangia 

 would naturally roll over, if they fell on the convex surface, and 

 settle on their lower face." This explanation is unsatisfactory 

 because it fails to take into account the fact that a discharged 

 sporangium is accompanied by a large drop of cell-sap and also 

 involves two unsound assumptions : (1) that, if a sporangium 

 strikes a vertical surface by its smooth rounded black surface only, 

 it will fall to the ground ; and (2) that a vertical surface must be 

 covered by a film of moisture to enable the sporangium to stick to 



1 Vide supra, p. 67. ^ Vide supra, pp. 65-66. 



3 W. B. Grove, loc. cit., p. 17. 



* Grove covered his culture with a bell-jar, on the inner surface of which 

 moisture was condensed. 



