THE DISPERSION OF THE SPORES 217 



It is clear, from the results just given and from our knowledge 

 of the size of spores in Hymenomycetes generally, 1 that for the 

 fruit-bodies of many species about a minute would be required for 

 the spores to fall from the gills to the ground. Even in the case 

 of Arnanitopsis vaginata, where the spores are unusually large in 

 addition to being spherical, about half a minute would be necessary. 

 For fruit-bodies of Polyporus, Polystictus, Fomes, Stereum, Corticium, 

 &c, growing on tree-trunks or dead branches some metres high, the 

 ground would only be reached after the spores had been falling 

 through the air for a period of time of the order of an hour. 



It seems certain that, owing to the alternation of day and 

 night and other meteorological causes, the air above the surface 

 of the earth is never quite still. The average speed of the air in 

 exposed situations is very considerable, amounting to miles an hour. 

 In woods and meadows, &c, where ground-fungi grow, the air- 

 movements are probably never less than some feet per minute, 

 and, as every one knows by experience, they are very frequently 

 much greater. Even when the air seems extremely still, so that 

 one cannot feel its motion and scarcely a leaf trembles on the 

 tallest trees, it is astonishing how complex and active are the 

 small convection currents and air-drifts that one may discover 

 near the ground, in gardens and woods, by the cautious liberation 

 of smoke or puff-ball dust. From what we know by experience 

 of air-movements, and from the calculations of the time that 

 would be required for spores to fall from their pilei to the ground 

 in perfectly still air, it seems to me to be an obvious conclusion 

 that the external air-currents, as a rule, are fully sufficient to 

 carry off the falling spores from beneath the pilei and to scatter 

 them broadcast. As a matter of fact in nature, unless a fruit-body 

 is confined by dense grass, loose leaves, or other natural obstacles, 

 one never finds any noticeable spore-deposit on the ground beneath 

 a pileus. For fruit-bodies of Stropharia semiglobata, Anellaria 

 separata, Coprinus comatus, or any other species growing in open 

 pastures, &c, it seems theoretically impossible that, if the wind is 

 blowing appreciably, any of the spores should settle on the ground 

 immediately beneath the pilei. 



1 Chap. XIV. 



