40 



RESEARCHES ON FUNGI 



can readily escape (B). If the tilt be increased to 2° 30', the critical 

 angle is reached (C) : 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 hymcnium and adhere there. With a tilt of 5° half the 

 spores are lost (D), and with a tilt of 9° 30' four-fifths of them (E). 

 The gills of a Mushroom are radially disposed, and it is therefore 

 evident that, if a Mushroom is tilted, those gills with their planes 



B 



i 



Fig. 12. — The effect of tilting the gills of Psalliota campeslris. Two irills are shown 

 in cross section. The arrows in the interlaruellar space indicate the paths of 

 the spores discharged in still air. A, gills in the normal position. In 13 the 

 gills are tilted 1° 30' from the vertical, in C 2° 30', in D 5°, and in E 9° 30'. 



most nearly perpendicular to the plane of tilt will suffer most, whilst 

 those with their planes most nearly parallel to the plane of tilt will 

 suffer least. The exact proportion of spores lost by a Avhole Mush- 

 room with a tilt of a ijiven anj^le Avould be somewhat ditiicult to 

 calculate, and no attempt will be made here to solve this pruhlem. 

 It is sufficiently clear, however, that when the pileus of one of the 

 AgaricineJB is tilted only a few degrees from its normal position, its 

 spore-liberating efficiency is greatly reduced. In this connection, it 

 is a distinctly significant fact that all hymenomycetous fruit-bodies 



