88 



RESEARCHES ON FUNGI 



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sporangium with greater accuracy toward the source of brightest 

 light. 



The drops excreted by the sporangium differ from those excreted 

 by the sporangiophore in that as they dry up they become brown 

 and ultimately as black as the subjacent sporangial wall (Fig. 43). 



This fact, which does not seem to 

 have been previously recorded, 

 lends support to Knoll's view 

 that the mucilage in the drops 

 excreted by the pileal hairs and 

 cystidia of Hymenomycetes, 

 the fruit-bodies of Pilobolus, etc., 

 is produced as a result of local 

 mucilaginisation of the cell-wall. 

 Knoll 1 supposed that the 

 drops are forced out of the 

 sporangiophore of Pilobolus 

 chiefly by turgor pressure, and 

 he suggested that their excretion 

 is a result of the operation of a 

 mechanism of the nature of a 

 valve which serves to prevent 

 the continual rise of the turgor 

 pressure and thereby to prevent 

 a premature discharge of the 

 sporangium. It may well be 

 that the excretion of drops is 

 concerned with the regulation of 

 the water and salt content and 

 the pressure equilibrium of the sporangiophore ; but that it is 

 specially concerned with preventing the premature discharge of the 

 sporangium seems very doubtful, for the drops begin to be excreted 

 on the naked stipe of the very young fruit-body long before the 

 sporangium or subsporangial swelling has been formed and some 

 twenty hours before the sporangium is to be discharged (Fig. 12, a 

 and b, p. 23). Moreover, similar drops are commonly excreted 



1 F. Knoll, loc. cit., p. 489. 



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• « • 



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Fig. 44. — Pilobolus longipes. Crystals 

 of calcium oxalate on : A, a piece 

 of the fringe of the wall of a dis- 

 charged sporangium, seen in face 

 view ; B, the black part of the spor- 

 angium-wall, seen in tangential 

 view ; C and D, the wall of the 

 subsporangial swelling and of the 

 stipe respectively, seen in face view. 

 Magnification, 1130. 



