4 8 



RESEARCHES ON FUNGI 



A fruit-body begins its existence in light or darkness as a 

 tiny papilla, directed at any angle to the substratum, but pro- 

 jecting more or less vertically from the surface of the stromatous 

 layer on which it is produced (Fig. 16, A). If developed in the 

 dark the papilla grows out into a long linger-like stipe, which 

 is perfectly indifferent to geotropic stimuli. In the course of 

 six weeks the stipe may attain a length of 15 cm. without showing 

 the least trace of a pileus (D), and sometimes it may become 

 branched (C). In weak light it is positively heliotropic and 



FlG. 16. — The forms of Lentinus lepideus. A, diagram showing the beginnings 

 of fruit-bodies as conical processes, c, arising on a stroma, s, developed on 

 wood. B, section of a normal fruit-body grown in light. C, sterile and 

 branched fruit-body found growing in darkness. D, sterile and finger-like 

 fruit-body after three weeks' growth in darkness. E, section of a fruit- 

 body with eccentric pileus. F, G, H, and I, branched and feebly-developed 

 fruit-bodies grown in weak light. All i natural size. 



thus reacts to this stimulus as if attempting to bring its free end 

 into the best illuminated position. When the tip of the stipe 

 is acted upon by light of sufficient intensity, it flattens and 

 expands in a symmetrical manner, and becomes converted into 

 a pileus. As soon as the development of this structure has been 

 initiated, a remarkable change takes place in the physiological 

 properties of the stipe. Whilst still barren, this was absolutely 

 without response to geotropic stimuli but was positively heliotropic : 

 it now becomes strongly negatively geotropic and entirely loses 

 its power of reacting to light. The rapidly developing pileus 



