50 RESEARCHES ON FUNGI 



We shall return to the problem of pileus eccentricity in con- 

 nection with Polyporus squamosus. It may, however, here be 

 pointed out that the power of response to the inorphogenic 

 stimulus of gravity varies much in different species of Hymeno- 

 mycetes. In Psalliota campestris, in Coprinus, and probably 

 quite generally in ground Agaricineae, it is not present at all; 

 in Lentinus lepideus and certain other comparatively long-stiped 

 Agaricinese it is slightly developed ; whilst in the relatively short- 

 stiped Pleurotus ostreatus and Polyporus squamosus, and in the 

 stipeless, bracket-shaped fruit-bodies growing on trees it is very 

 marked. 



From the above it seems clear that the fruit-bodies of Lentinus 

 lepideus possess in a high degree the power of adjusting themselves 

 in a manner suited to their environment. In nature it sometimes 

 happens, as I have once observed, that a fruit-body begins its 

 development on the underside of a log or other mass of wood. 

 Even then it can still succeed in placing its gills in their optimum 

 position. 



Psalliota campestris. Mushrooms were first of all studied as 

 they came up under natural conditions in a large pasture. The 

 actual amount of curvature which the stipes of the fruit-bodies 

 investigated had undergone in extreme cases during development 

 may be gathered from Fig. 17, in which some field sketches have 

 been reproduced. The curvatures had been sufficient to place 

 the planes of all the pilei in a horizontal position. However, in 

 older Mushrooms, it was found that the stipe only acts as a coarse 

 adjustment for the gills. The latter are very thin, fairly deep, 

 and closely packed; and the fine adjustment of their planes in 

 exactly vertical directions can only be effected by their own 

 delicate reactions to the stimulus of gravity. 



When an accident happens to a mature Mushroom so that it 

 becomes tilted, as is often the case in pastures where horses and 

 cattle are browsing, the stipe and pileus remain fixed in their 

 new positions. However, the gills are still in a most sensitive 

 condition and quickly respond to the stimulus of gravity. Each 

 gill grows faster on its upper side than on its lower side and 

 thus gradually curves downwards, so that a large part of it comes 



