38 RESEARCHES ON FUNGI 



ensures that the very narrow hymenial tubes shall be kept exactly 

 in the vertical position. The importance of this is obvious when it 

 is realised that even a very slight tilt of the tubes would prevent the 

 spores from escaping from them. 1 Further, the fruit-bodies can 

 withstand uninjured the severest frosts of winter, and, judging from 

 some experiments made with Fomes igniarius, can recover after pro- 

 longed desiccation. 2 Lastly, they have extremely narrow hymenial 

 tubes. This, as we have seen, involves a great increase of spore- 

 bearing surface. Taking into account the manner in which the 

 spores are discharged from the basidia in Polyporese (Fig. 66, p. 189), 

 it would seem that for F. vegetus and F. igniarius the width of the 

 tubes is so small that, after allowing for a small margin of safety, 

 it has almost, if not quite, reached its limit. 



The more liable a polyporaceous fruit-body is to become slightly 

 tilted, owing to developmental changes, transpiration, the accumula- 

 tion of rain-water on its upper surface, the visits of birds, &c, the 

 greater is the advantage of wide hymenial tubes over narrow ones in 

 liberating the spores. Perhaps it is for this reason that the tubes in 

 the soft and wide-spreading brackets of Folyporus squamosus are of 

 considerable width, so that they stand in marked contrast with those 

 of the more compact and extremely rigid fruit-bodies of Fomes 

 igniarius, &c. The dimensions of the tubes in these and other 

 species seem to me, at least to a certain degree, to be correlated with 

 the nature of the pileus flesh. 



1 With the beam-of-light method (vide infra, Chap. VII.) it was observed that 

 when the tubes of Polystictus hirsutus were tilted to an angle of 15° from the 

 vertical, there was a marked diminution in the number of spores liberated, and 

 that with a tilt of 30° spore-liberation almost entirely ceased. 



2 Specimens which had been gathered and kept dry for six months began to 

 grow on their undersides when they were placed in a damp-chamber. 



