FALCK'S THEORY 219 



been killed by heating. Falck believes that " the fruit-bodies pro- 

 duce heat not to raise their own temperature but to warm the layers 

 of air beneath the pilei." l He considers that the heat thus given off 

 creates convection currents in which the spores are borne away from 

 the pilei. In support of this, Falck has described experiments in 

 which spore-deposits were obtained from pilei which had been 

 suspended in closed glass vessels. He found that the spores were 

 carried up and down in the glass vessels so that they settled upon 

 ledges placed both above and below the pilei. Falck has followed 

 out his idea still further. After showing that the presence of 

 maggots leads to an appreciable increase in the temperature of 

 insulated pilei. he came to the following theoretical conclusions. 

 Tlje pileus flesh of large Agarics has become specially thickened and 

 laden with food substances for the purpose of feeding maggots. The 

 maggots respire actively and thus produce heat, which is added to 

 that resulting from the respiration of the pileus, and is made use of 

 for increasing the convection currents which bear away the spores 

 in the neighbourhood of the gills. We thus have a symbiotic 

 relationship between hymenomycetous fruit-bodies and flies. 



It must be admitted that Falck's theory is a very ingenious one. 

 However, I am not sure to what extent we are justified in drawing 

 conclusions from the laboratory experiments as to what actually 

 happens in fields and woods. Proof has yet to be brought forward 

 that in nature the pilei become sufficiently warmed to produce 

 effective convection currents. If the ordinary air-currents in fields 

 and woods are never less than a few feet per minute, and are usually 

 much greater, it seems to me that they must be so active in carrying 

 away the spores from the fruit-bodies that the convection currents 

 arising from the very slightly warmed condition of the pilei can be 

 only quite insignificant, and therefore ineffective, in comparison. 

 From this consideration it seems that in nature the heat produced 

 by a pileus must be generally useless and unnecessary for the purpose 

 assigned to it by Falck. 



When the wind is blowing, transpiration becomes active. Pos- 

 sibly the loss of heat from a fruit-body thereby occasioned, counter- 

 balances the gain by respiration. Falck's theory would be placed on 

 1 Loc. cit., p. 32. 



