BY D. McALPINE. 555 



As far as has been determined, the conditions which influence 

 the production of light are the following : — 



1. It is only in the living organism that the phenomenon 

 occurs, and the greater the vital activity the more marked is the 

 phosphorescence. Brefeld* observed in the mycelial strands of 

 A. mellea that only the youngest and softest portions were phos- 

 phorescent, while the older brown and hard strands were no 

 longer capable of it. 



2. Oxygen is necessary, for as soon as it is withdrawn the 

 luminosity ceases, but it reappears when the air is restored. In 

 pure oxygen the light does not become more intensive. 



3. Phosphorescence is also dependent on the temperature. 

 There is a minimum below which the light immediately ceases, 

 and a maximum of luminosity beyond which temperature the 

 light decreases until the heat is sufficient to kill the fungus, and 

 then the luminosity is gone for ever. It appears that the mini- 

 mum, the optimum and the maximum may vary in the same 

 fungus according to its vital activity. 



4. As regards moisture, the luminosity does not appear to be 

 affected by wet or dry weather. I immersed a small portion of 

 the gills of P. candescens in water for an hour and a half, and the 

 light was practically the same at the end of that time. 



Phosphorescence has been proved to be due to minute organ- 

 isms — the photogenic bacteria — in the case of sea fish and animal 

 flesh, but although bacteria are present on the gills of this fungus 

 they have nothing to do with the phosphorescence. It will be 

 noted that the luminous bacteria occur on flesh and the carcases 

 of fish and are living organisms, just as the fungi are only 

 phosphorescent while alive. It was concluded by Fabref that 

 phosphorescence is the result of the respiratory activity of the 

 fungus, but that would hardly account for the phenomenon being 

 restricted to certain parts nor for its being confined to so few 

 forms of fungi. Even if due to a temporary increase of oxidation 

 the exciting cause of such increase would require explanation. 



* Schimmelpilze iii., p. 171. 

 t Ann. Sci. Nat. Series iv. Vol. 4 (1853). 



