A Fluorescent Colouring Matter. H. Wager. 163 



absorb the more refrangible, blue and violet, rays of the spec- 

 trum, which have a deleterious action upon protoplasm, they 

 may exercise a protective function against a too intense light*. 



The light energy absorbed by the pigments may also be of 

 use in maintaining the tissues at a suitable temperature in 

 order that the metabolic activities of the Fungus may be 

 carried on satisfactorily. 



One of the important functions of the Fungus pigments 

 appears to be to render the tissues more resistant. The 

 coloration of the non-gelatinous cell membranes is accom- 

 panied with increased firmness, and in most cases with excep- 

 tional power of resisting the action of concentrated sulphuric 

 acid, phenomena which recall the similar behaviour of the 

 sclerosed, lignified and suberised membranes of the higher 

 plantsf. This is well seen in coloured spores the membranes 

 of which, as compared with those of colourless spores, are 

 ver^;^ resistant to the action of concentrated sulphuric acid. 



No physiological or biological explanation of the fluorescent 

 pigments can be given. Nor can any explanation be given of 

 phosphorescence which also occurs in some Fungi. Both 

 phosphorescence and fluorescence are now classed together as 

 photo-luminescence, and both are due to the stimulus of the 

 light absorbed. Phosphorescent substances are those which 

 continue to emit light for some time after the stimulus is with- 

 drawn ; fluorescent substances only emit light during the time 

 the stimulus is acting. 



A light yellow alcoholic solution of the pigment of Leptonia 

 incana shows a beautiful green colour when a beam of sunlight 

 is passed through it. If, instead of white light, a beam of 

 violet or blue light is allowed to pass through, the same green 

 colour is observed, and the invisible ultra-violet rays are also 

 able to produce the same effect. The blue, violet or ultra- 

 violet rays on being absorbed by the solution at once set up 

 disturbances in the colouring matter by which light of a different 

 wave-length is emitted. Stokes stated that the wave-length 

 of the fluorescent radiation is always longer than that of the 

 radiation which excites fluorescence. Recent investigations 

 have however shown that this is not always the case, and 

 according to Nichols the absorption band, to which fluorescence 

 is due, and the fluorescent spectrum overlap, and all the waves 

 included in the absorption band can produce the excitation. 

 The yellow fluorescent solution of Leptonia incana shows a 

 strong absorption at the more refrangible end of the spectrum 

 extending from the extreme violet to about the line E and 



* Cf. Duller, Researches on Fungi. 



t De Bary, Comparative Morphology and Biology, etc., of the Fungi. 



