PSALLIOTA CAMPESTRIS 375 



downwards. If, owing to insufficient rigidity of the whole fruit- 

 body, the lamellae w r ere permitted to oscillate about their normal 

 positions, or if the pileus were suddenly tilted, a very large number 

 of spores after being shot away from their sterigmata would, on 

 falling, touch the sides of the lamellae, adhere there, and never 

 escape into the free air beneath the pileus. In an investigation 

 upon some fruit-bodies with gills having a depth of 5 mm. the 

 following facts were elucidated. When the median planes of the 

 gills are tilted about their lines of attachment to the pileus to an 

 angle of 1 30' from the vertical, the spores can all escape down 

 the interlamellar spaces. If the tilt be increased to 2 30', the 

 critical angle is reached : all the spores can still make their way 

 out between the gills, but with any increase in the tilt some of them 

 fall upon the hymenium and adhere there. With a tilt of 5 half 

 the spores are lost, and with a tilt of 9 30' four-fifths of them. 1 

 These particulars serve to emphasise the necessity for consider- 

 able rigidity in the fruit-body as a whole. 



The rigidity of the stipe is due in part to the turgidity, density 

 of arrangement, and mode of adherence of the long strings of hyphae 

 making up its substance, but in part also to the fact that the stipe 

 as a whole tends to have the form of a hollow cylinder. 2 In one 

 variety of Mushroom which I cultivated in England, the core of 

 the stipe was always distinctly hollow. 3 In the wild Mushroom the 

 core is either hollow or stuffed with loose fibrils. 



The firm and massive pileus-flesh, constructed of evenly-woven 

 plectenchyma, is important from the mechanical point of view in 

 that it supports the gills and keeps them fixed in a constant position 

 during the several days of the spore-discharge period ; but it also 

 has other functions : it serves to conduct nutriment to the gills 

 during their development and constitutes a reservoir of water 

 upon which the gills may draw according to their needs when they 

 have attained maturity. 



The form of the fruit-body of the Mushroom, or indeed of that 

 of any other typical terrestrial agaric such as Lepiota procera, from 

 the mechanical point of view, appears to be, within limits, the most 



1 Vol. i, pp. 39^0. - Vol. i, pp. 



3 Vol. i, Fig. 17. A and B, p. 51. 



