386 RESEARCHES ON FUNGI 



I scraped away the gills with a sharp penknife, and the pileus-flesh 

 still continued to glow, although quite feebly. 



When the fruit-body begins its development as a tiny rudiment 

 on the exterior of a block of wood, it is brightly luminous all over 

 its surface. As differentiation proceeds, light is emitted not merely 

 by the rudimentary pileus but also by the enlarging stipe. As 

 soon as the stipe has become full-grown, it ceases to give out light, 

 and then only the developing pileus is luminous. For some time 

 the pileus gives out light from both its surfaces, although more 

 strongly from its under surface. Then the luminescence becomes 

 concentrated in the gills alone, where the production and liberation 

 of spores is still in active progress ; and, finally, as the hymenium 

 becomes more and more exhausted, even the light emitted by the 

 gills grows dim and disappears. It therefore seems that the in- 

 tensity of the light given out by any part of a fruit-body is directly 

 proportional to the rate of development. The emission of light by 

 the hyphae of Panus stypt. luminescens, like the emission of heat 

 during respiration, is (as we shall see) an oxidative process ; and, 

 like the emission of heat during respiration, it appears to increase 

 in intensity with an increase in the rapidity of growth, and vice 

 versa. 



The colour of the light emitted by Panus stypt. luminescens has 

 always appeared to me to be greenish. There is certainly no red 

 in it. When working in the dark-room I found that, after using 

 a red light and then switching it off, I could at once perceive the light 

 of the fungus, whereas after using a white light perception only took 

 place with some delay. The more favourable result with the red 

 light seems to have been due to the fact that a red light does not 

 tire one's eyes for seeing a green light. 



When one's eyes are in a sensitive condition, it is possible to 

 perceive the light given out by the under side of a group of fruit- 

 bodies at a distance of several feet. When about six fruit-bodies 

 were set together in a dark laboratory, I could clearly see the light 

 which they gave out at a distance of 10 feet and just perceive the 

 light at a distance of even 30 feet. 



A fruit-body is most strongly luminous when it is just full-grown. 

 Thereafter, as it exhausts itself by shedding spores its light gradually 



