222 RESEARCHES ON FUNGI 



tion in the same manner as the hymenomycetous fruit-bodies in 

 Falck's experiments. The metabolism which leads to the production 

 of a billion or more spores in a Giant Puff-ball in the course of a few 

 days, must be very considerable. For the present, at least, I am not 

 inclined to look upon the heat arising in the pilei as in any way 

 surprising in amount or as being more than incidental in character. 



Although Falck's theory seems to me to require some modifica- 

 tion, and in any case to be of limited application, its promulgation 

 has certainly raised an important question. The fruit-bodies of 

 certain species of Boletus, Amanita, Paxillus, &c., have broad pilei 

 and comparatively short stipes; and they often come up, half 

 concealed in grass or loose leaves, in hollows, dense woods, or other 

 protected places. Here the air, immediately beneath the gills, on 

 quiet days must be at its stillest. We require to know whether 

 under such circumstances, owing to physical or metabolic changes 

 going on in the fruit-bodies, convection currents arise from the 

 latter capable of carrying the spores between the surrounding 

 obstacles and lifting them to such height that they pass into more 

 active air-currents in motion above the herbage or forest floor. 

 This ought to be determined by direct observation in nature. 

 Should such convection currents be discovered, it would then be 

 necessary to find out to what extent they were brought about by 

 radiation, transpiration, or the giving off of heat due to respiration. 

 If the air surrounding a fruit-body were ever quite still, any con- 

 vection currents arising from the pileus, in order to raise the spores 

 above the pileus, would require to have an average upward velocity 

 of 1-6 mm. per second according to the size of the spores. 



Beam-of-light and other observations of my own have served 

 to corroborate Falck's discovery, that exceedingly faint convection 

 currents, such as one can never feel, are capable of transporting 

 the spores of Hymenoinycetes with astonishing ease. Even in 

 large closed beakers it is exceedingly difficult to reduce the air 

 to anything like real stillness. Small convection currents can 

 certainly be produced with a very small expenditure of energy. 

 Whether sufficient can be given off by a large fruit-body to be of 

 use under special circumstances remains to be determined. If 

 this should prove to be the case, we could draw the conclusion 



