ADJUSTMENTS OF FRUIT-BODIES 61 



The shape of the pileus seems to be partly decided by the 

 direction of the conical process upon which it develops. When 

 a conical process happens to point vertically upwards (as it very 

 rarely does), the stipe to which it gives rise is vertical and the 



FlG. 22. Polyporus squumosus. Under surface of a large fruit-body with a central 

 stipe. J natural size. 



pileus horizontal from the moment of their differentiation (cf. 

 Plate V., Fig. 35). Under these circumstances, since the internal 

 developmental forces are symmetrically disposed, the pileus simply 

 grows at an equal rate all round its periphery. In response to 

 a diageotropic stimulus, it spreads itself out in a horizontal plane. 



