56 RESEARCHES ON FUNGI 



The adjustments by which the hy menial surfaces are placed in 

 the optimum position for spore-liberation in the Mushroom are no 

 less than four in number, and may be summed up as follows : 

 (1) Turning the pileus into an erect position by an upward 

 curvature of the stipe ; (2) raising the pileus several centimetres 

 above the ground by growth in length of the stipe ; (3) placing 

 the gills with their long axes horizontal by an expansion of the 

 pileus (Fig. 19); and (4) setting the planes of the gills in hori- 



FlG. 19. Psalliota arvensis. a-d, sections of four fruit-bodies showing suc- 

 cessive stages in the raising of the gills into a horizontal position by the 

 expansion of the pileus. At a the gills are still enclosed in the large gill 

 chamber. All natural size. 



zontal positions by the turning of the gills themselves about their 

 directions of attachment to the pileus flesh. Whilst the erection of 

 the pileus and the turning of the gills coarse and fine adjustments 

 respectively are controlled by the external stimulus of gravity, the 

 raising of the pileus and its expansion are, doubtless, due to internal 

 developmental forces alone. Proof of the latter statement seems to 

 be afforded by the fact that Mushrooms can elongate their stipes 

 and expand their pilei when growing upside down in the dark 

 (cf. Fig. 17, A). 



Polyporus squamosus. 1 P. squamosus, the Great Scaly Poly- 



1 Cf. Buller, "The Biology of Polyporus sqtiamosus, a Timber-destroying 

 Fungus," Journ. of Economic Biology, 1906, vol. i. pp. 101-138. 



