ADJUSTMENTS OF FRUIT-BODIES 65 



cannot hinder the fall of the spores, or then* dispersion by the 

 wind. 



We may now sum up the adjustments made in a developing 

 fruit-body by which the hymenial surfaces are placed in the 

 optimum position for spore-discharge. They are five in number : 



(1) Slight raising of the pileus by growth in length of the stipe; 



(2) placing the top of the pileus in a horizontal plane by a curvature 

 of the stipe ; (3) growth of the pileus parallel to the earth's surface ; 

 (4) growth of the pileus with a symmetry suited to the position of 

 the stipe ; and (5) the downward growth of the hymenial tubes. 

 The first of these adjustments is doubtless due to internal develop- 

 mental causes alone, but the other four are controlled by gravity. 



A fruit-body of Polyporus squamosus owes the origin of its pileus 

 to the stimulus of light, and in addition it responds in four different 

 ways to the stimulus of gravity. On the other hand, a Mushroom is 

 indifferent to light and has only two reactions to gravity. The 

 difference between the two species in the number of responses made 

 to external stimuli is correlated with the fact that the one fungus 

 grows on a tree and the other on the ground. In each case the 

 dependence on external forces seems to be of the simplest kind 

 to meet the requirements of the environment in a successful 

 manner. 



Coprinus plicatilis. — The small fruit-bodies of this species were 

 found coming up on a lawn. A single specimen with its surrounding 

 turf was taken indoors, and immediately placed on its side in the 

 position shown at a in Fig. 24. In order to prevent too rapid 

 transpiration, the turf was sprinkled with water and covered with an 

 inverted glass dish. In two hours the plane of the pileus had been 

 turned by the stipe through an angle of 60° (b), and in three hours 

 it had become almost horizontal (d). To my surprise, however, the 

 stipe continued its curvature for an hour, until the pileus had become 

 tilted quite 20° too much (/). It then began to bend back again, and 

 in the course of a further hour the pileus was returned for the second 

 time to its optimum position (A). The curvature of the stipe, how- 

 ever, still continued, and became overdone to the extent of about 

 15° (jf). Again the stipe rebent itself, and for the third time the 



pileus became erect (on). After this the stipe overdid its curvature 



E 



