220 RESEARCHES ON FUNGI 



a much firmer basis if it could be shown that out in the open the 

 temperature of fruit-bodies becomes appreciably higher than that of 

 the surrounding atmosphere, but this has not yet been done. For 

 Polyporus squamosus (Fig. 1) and other fruit-bodies growing on 

 trees, where air-currents are never absent and the free space below 

 the pilei is usually great, for small or thin fruit-bodies such as those 

 of Mycena, Galera, Schizophyllum, Corticium, Stereum, and Poly- 

 stictus, and also quite generally for all fruit-bodies during weather 

 which is at all windy, the unimportance of any very slight warming 

 of the pilei seems to me to be obvious. 



As a rule, in nature, it is impossible to see what happens to 

 spores on leaving the pileus. Otherwise a direct test might quickly 

 be applied to Falck's theory. However, in the case of Polyporus 

 squamosus, as described in Chapter VI., I have been able to see the 

 spore-clouds leaving a large fruit-body growing on a log. The log 

 was placed in a closed greenhouse, where the air was so quiet that 

 one could not feel that it was moving. As the spores emerged from 

 the hymenial tubes, they were carried along the underside of the 

 pileus in one direction by a very slow air-current moving at the rate 

 of a few feet per minute. The spore-clouds could be seen to drift 

 laterally to a distance of 2 metres from the fruit-body. Whilst 

 doing so, they were gradually broken up by small but very complex 

 convection currents, the presence of which was only revealed by the 

 spore-movements. As the spore-cloud moved outwards from the 

 edge of the pileus, it showed no tendency to pass upwards. In the 

 course of several hours, nothing happened to suggest that the fruit- 

 body was giving off so much heat that it produced convection 

 currents of importance in scattering the spores. It seems to me that 

 these observations are distinctly adverse to Falck's theory, for they 

 not only show that, even when the air seems very still, quite slow 

 air-currents due to external causes are of the greatest importance 

 in carrying the spores from beneath a pileus, but also that the con- 

 vection currents produced by a large pileus may be practically 

 inappreciable when this is not insulated. 



However, it might be argued that the fruit-body was a solitary 

 one ; that Polyporus squamosus frequently produces from four to ten 

 sporophores in a densely imbricated cluster ; that the space between 



