42 RESEARCHES ON FUNGI 



bodies, e.g. those of Mycena epipterygia, have a distinct advantage 

 over thick-stiped, such as those of Russula emetica, in that, if the 

 fruit-body should be even considerably displaced by any accident, 

 it can quickly be set once more with the gills in vertical planes by 

 means of a suitable geotropic curvature of the stipe. With Russulse, 

 Psalliotse, &c, owing to the thickness of the stipes, this is impossible 

 when the pilei have become outstretched. In these cases, the gills 

 themselves react to the stimulus of gravity, and after a slight dis- 

 placement of the fruit-body, quickly readjust themselves so as to 

 come to lie in vertical planes once more ; but when the displacement 

 is considerable, this remedy becomes of very little avail. In species 

 of Galera, Mycena, &c, the structure of the stipe is such as to remind 

 one of the hollow peduncle which supports the capitulum of a 

 Dandelion or the pith-filled one of a Chrysanthemum. It is clear 

 that for the stipes of Agaricineae we have a series of variations 

 in the cylindrical form comparable with that found in the stems of 

 Phanerogams and bearing a similar interpretation. 



A certain amount of rigidity is given to many stipes, not merely 

 by their cylindrical form, but also by longitudinal tensions set up 

 in the layers of hyphae of which they are composed. The existence 

 of these tensions can easily be proved by partially bisecting or 

 quadrisecting the stipes concerned, e.g. those of Coprinus comatus, 

 Mycenae, &c, in a longitudinal direction from below upwards, with 

 a knife. The halves or quarters so produced bend outwards and 

 resist attempts to replace them in their original positions (Fig. 13). 

 It is well known that similar tensions occur in the young stems 

 of the Higher Plants. 



The foregoing remarks tend to show that stipes in general are 

 well adapted to give the basidia the best possible chance of dis- 

 charging their spores, so that they may freely escape from the 

 fruit-body. There can be no doubt that the pileus flesh is adapted 

 to the same end. Its function is not merely to support the weight 

 of the gills or! hy menial tubes, but to hold them fixed in one 

 particular position. As one might expect from a very simple 

 mechanical consideration, the pileus flesh is always thickest toAvard 

 the centre and thins out rapidly in the peripheral direction. Its 

 exact form and the materials of which it is composed vary much 



