34 RESEARCHES ON FUNGI 



gills are shallow, and the interlamellar spaces required to provide 

 room for the free development of the basidia and spores are secured : 

 in part by the rigidity of the gills, in part by a suitable spacing of 

 the gills where they adjoin the flesh and at their margins close to 

 the stipe, and in part by the cystidia which act as guards and prevent 

 two adjacent gills from anywhere touching one another with their 

 hymenial surfaces. 



(4) The cystidia do not connect adjacent gills during spore- 

 discharge. When spore-discharge is about to begin, the pileus 

 expands, with the result that adjacent gills become widely separated 

 from one another. At this stage of development all the cystidia 

 project from the gills as pegs. 



(5) The pileus-flesh covering the gills is membranous and is 

 provided with grooves which run radially above the longer gills. 

 When the pileus expands just before and during spore-discharge, 

 these grooves open out. As expansion of the pileus proceeds, the 

 grooves are deepened so that the longer gills become split down 

 their median planes for a certain distance. The result is that the 

 expanded pileus, when seen from above, much resembles a parasol. 

 Owing to the opening of the radial grooves and the splitting of the 

 shallow gills for a certain distance down their median planes, the 

 upper part of each long gill becomes widely V-shaped in cross 

 section and each gill as a whole Y-shaped in cross-section. Owing 

 to this change of form in the gills duruig the expansion of the 

 pileus, a large part of the hymenium comes to look downwards 

 towards the earth. This is distinctly of advantage in enabhng the 

 spores to escape from the fruit-body, and in a considerable measure 

 it compensates for the lack of autodigestion of the gills. Spore- 

 discharge commences only after the fruit-body has become expanded 

 like a parasol. 



(6) The basidia are irregularly dimorphic-trimorphic. The 

 longest basidia are the most protuberant, the shortest practically 

 non-protuberant, while the intermediate have an intermediate 

 protuberancy. In the zone of spore-discharge there are from two 

 to three sub-zones of spore -discharge corresponding to the irregular 

 dimorphic-trimorphic grouping of the basidia. 



(7) In an unexpanded fruit-body the pileus-flesh descends a 



