392 RESEARCHES ON FUNGI 



the developmental and nutritional points of view, it also seems 

 fitting that the gills should become shallower and shallower 

 as the pileus-flesh immediately above them becomes progressively 

 diminished in thickness beyond a certain point. 



The narrowing of the gills in the neighbourhood of the stipe has 

 an entirely different significance from the narrowing at the pileus- 

 periphery. The gills are cut away from the stipe in such a way 

 as to permit of their being raised through an angle of about 90 

 during the rapid expansion of the pileus, without their being 

 subjected to strains which would tear them. The question of the 

 relation of the gills to the stipe in Agaricineae in general, however, 

 will be dealt with more fully in Volume IV. 



The Gill-chamber and the Annulus. The gills of a Mushroom 

 are protected during their development and during the first stages 

 of the expansion of the pileus by being enclosed in a gill-chamber. 

 The wall of this chamber at the top and sides consists of the pileus- 

 flesh and at the bottom of the velum partiale (Fig. 134, C, p. 377 ; 

 also Fig. 140, D, F). As the pileus expands, the floor of the gill- 

 chamber becomes drawn out horizontally into an extended but very 

 thin and fragile membrane which, with further stretching, breaks, 

 so that fragments of the velum are carried away upon the edge of 

 the pileus (Fig. 137, p. 383) and an annulus is left surrounding the 

 stipe (Fig. 134 ; also Fig. 140, A, B, H, I). The base of the thin 

 membrane which closes the gill-chamber during the earlier stages of 

 expansion, is, at its origin, a tubular structure ensheathing and 

 apparently forming part of the outside of the stipe enclosed within 

 the chamber. This sheath is pulled away from the stipe from below 

 upwards during the expansion of the pileus (Fig. 140, B, C, E, F). 

 The region of the stipe from which the sheath has been pulled can 

 be distinguished in some field Mushrooms by its roughened surface, 

 which indicates where cleavage took place : to its upper edge the 

 annulus is attached, while at its lower edge there is not infrequently 

 a trace of a second ring (Fig. 140, A). The origin of the roughened 

 region and of the two annuli may best be realised by a reference 

 to the semi-diagrammatic drawing given in Fig. 140, B, where 

 the arrows indicate the movements which have taken place. 

 Fig. 140, E, shows the exterior of a young Mushroom in which the 



