ADJUSTMENTS OF FRUIT-BODIES 55 



up against soil, grass, or dung, &c, in such a manner that con- 

 siderable resistance is offered to the free expansion of the pilei. 

 The chief effect of an unusual lengthening of the stipe upon a 

 fruit-body as a spore-producing organ, consists in increasing the 

 chances of the pileus being raised to such a height that it becomes 

 freed from obstacles and can successfully liberate its spores. 



Light gives rise in a Mushroom neither to a heliotropic nor 

 to a morphogenic reaction. I have been unable to detect any 

 heliotropic curvatures of the stipes of fruit-bodies grown on artificial 

 beds of horse manure, and a special experiment with wild Mush- 

 rooms also gave negative results. Eight pieces of turf, containing 

 Mushrooms in an early button stage of development, were taken 

 up from a field and placed in a room in such a way that the 

 buttons were well lighted on one side and in strong shadow upon 

 the other. However, the stipes grew up vertically and exhibited 

 no signs of bending toward the source of light. That Mushrooms 

 do not give a morphogenic reaction to illumination may be deduced 

 from the fact that they develop in form equally well in a perfectly 

 dark cellar and in a sunlit field. 



The development of the fruit-bodies of Lentinus lepideus is 

 controlled by light and gravity in succession, whilst those of 

 Psalliota campestris react to gravity alone. This difference 

 seems to me to be connected with the diversity in the habitats 

 of the two species. Lentinus lepideus is a wood fungus. The 

 orientation of the surface of its substratum is indefinite, and may 

 be most varied in respect to the fruit-bodies. Response to both 

 light and gravity under these circumstances is, as already explained, 

 of distinct advantage. On the other hand, Psalliota campestris is 

 a ground fungus. The orientation of its substratum is in so far 

 definite that the surface is on the average horizontal. This being 

 so, when a fruit-body has once begun to form on the surface of 

 the ground, a negative geotropic reaction alone is sufficient to 

 enable the stipe to raise the pileus and bring it into the optimum 

 position. Hence, we find that the development of the Mushroom 

 is regulated from without simply by the stimulus of gravity. No 

 advantage would be gained by sensitiveness to light, and indifference 

 towards it is therefore easily understood. 



