CHAPTER III 



THE FUNCTIONS OF THE STIPE AND OF THE PILEUS FLESH— 



THE GILL-CHAMBER 



The meclianics of the stipes of the more complex Hymenomycetes 

 might well form the subject of an interesting and a detailed investi- 

 gation. A few remarks may here be made in this connection upon 

 the stipes which are centrally situated beneath radiate pilei in the 

 most highly developed fruit-bodies. The stipe can support the 

 pileus with far less strain in a centric than in an eccentric position, 

 and it seems probable that this mechanical principle has been one of 

 the chief factors in brinuinj? about the evolution of the umbrella 

 form of Agaric. In different species stipes vary much in length, 

 thickness, and in the nature and disposition of the materials of Avhich 

 they are composed ; but no doubt there is always a correlation, and 

 often a close one, between their structure and the work which they 

 have to do in supporting the pileus at a distance from the ground, 

 and in keeping the gills in exactly vertical planes. 



When one realises how very important it is, from the point of 

 view of spore-liberation, that the planes of gills, the axes of hymenial 

 tubes, &c., should be kept quite motionless in a vertical position, one 

 cannot be surprised to find that the mechanical structure of the 

 stipe and pileus flesh is such as to give the whole fruit-body a 

 remarkable amount of stability. Were the gills of Agaricinese, or 

 the hymenial tubes of Polyporefe, subjected to even slight continuous 

 tilting movements, it is certain that a great proportion of the spores 

 could never be liberated — for after discharge from their basidia, vast 

 numbers of them would strike and adhere to the hymenium. In the 

 Mushroom, for example, it has been found ^ that in still air the paths 

 of fall of the spores in the interlamellar spaces are as shown in 

 Fig. 12, A. When the planes of the gills are tilted 1° 30', the spores 



1 Vide infra, Chap. XVII. 



39 



