376 RESEARCHES ON FUNGI 



daylight while mine had been rested, I perceived the hght from the 

 fungus lamps much more quickly than he could. 



The above series of experiments shows very clearly that the 

 length of time one needs to spend in the dark-room before per- 

 ceiving the light given out from a luminous fungus depends on the 

 sensitiveness of the eyes to weak illumination or, in other words, 

 on their adaptation to darkness, and varies roughly from to 15 

 minutes. A recognition of these facts is of some interest, for there 

 can be but little doubt that certain mycologists have failed to see 

 the light given out by a luminous fungus taken into a dark-room 

 because they did not wait in the dark-room sufficiently long to 

 allow their eyes to acquire the necessary sensitiveness to feeble 

 illumination. In testing a new fungus for luminosity, one ought to 

 carry on observations in the dark-room for at least 15 minutes. 



The fruit-bodies of Panus stypt. luminescens are very small com- 

 pared with those of Pleurotus japonicus or Clitocybe illudens. Never- 

 theless, in nature, the light which they give out is not inconsiderable 

 and may make them conspicuous at night. Dr. G. R. Bisby has 

 informed me that once in Minnesota, when walking in a wooded 

 place in the dark, he discovered a cluster of the fruit-bodies simply by 

 having his attention drawn to them by the light which they emitted. 



The only plants known to produce light are certain Bacteria, 

 certain Peridinieae, certain strains of the Ascomycete Xylaria Hypo- 

 xylon} and the Hymenomycetes enumerated above. There do not 

 appear to be any luminescent Phycomycetes, Gastromycetes, or 

 Fungi Imperfecti. 



Luminescent bacteria are very widely distributed and about 

 thirty species are already known.^ They cause the luminescence 

 often seen at the surface of damp bones, butcher's meat, sausages, 

 marine fish, the dead bodies of land animals, human corpses, etc. 

 Mohsch made pure cultures of Bacterium phosphoreum upon a 

 medium containing sodium chloride, peptone, and glycerine, and 

 solidified with agar or gelatine (Fig. 166). By spreading the 

 nutrient medium over the inner side of conical flasks of one or two 

 litres capacity, he succeeded in making bacterial lamps (Fig. 167, 



1 Vide infra, p. 416. 



2 Hans Molisch, Leuchtende Pflanzen, Jena, 1904, p. 84. 



