BIOLUMINESCENCE IN FUNGI 373 



diarrhoea." C. illudens appears to be absent from central Canada, 

 but it is known to occur in eastern Canada. Whilst at Toronto 

 Dr. J. H. Faull once showed me a splendid cluster of living fruit- 

 bodies which he had collected in a near-by wood. 



Murril ^ examined for luminosity some fruit-bodies of Clitocybe 

 illudens, as well as wood containing the mycelium, on two successive 

 days, and noted that he was obliged to remain in the dark for some 

 time before he could perceive any luminescence : on August 21, at 

 1.30 P.M. for 7 minutes, at 7.30 p.m. for 1-5 minutes ; on August 22, 

 at 9 A.M. for 10-15 minutes, at 9 p.m. for 1-2 minutes. These facts, 

 upon which Murril makes no comment, are easily understood on the 

 supposition (1) that the luminous fruit-bodies, like those of Panus 

 siypt. luminescens, etc., give out, both in daylight and in darkness, 

 a steady continuous light, and (2) that the variable factor is the 

 physiological condition of the eyes of the observer. The length of 

 time one is obliged to wait in a dark room before observing the soft 

 glow of a luminous fungus depends simply upon the sensitiveness of 

 the eyes for the perception of relatively very feeble rays of light. 

 The longer one has been exposed to strong daylight, the longer one 

 is obliged to remain in the dark-room before perceiving lumines- 

 cence, and vice versa. In the morning when the sun is up, especially 

 in summer-time, one's eyes lose rapidly and in a high degree their 

 adaptation for seeing weak lights in the dark ; whilst in the evening, 

 when the sun is decHning, or has declined, below the horizon, one's 

 eyes are regaining, or have regained, their sensitiveness. Hence, 

 as a rule, one perceives luminous fungi in the dark more rapidly in 

 the evening than in the morning or at noon. 



It will be shown in a later Section that the mycelium of Panus 

 stypt. luminescens is luminous and gives out a very steady and con- 

 tinuous light for many successive weeks or months. Using Birch- 

 block cultures as fungus lamps (c/. Fig. 170, p. 391), I made a series 

 of experiments to determine the length of time it was necessary for 

 me to remain in the dark-room before perceiving the light emitted 

 by the fungus. The experiments were all carried out at Winnipeg 

 on April 17, 1923. 



(1) I arose at 4 a.m. and, while it was still dark, walked to the 

 ^ W. A. Murril, "Luminescence in Fungi," Mycologia, vol. vii, 1915, pp. 132-133. 



