1893.J 



A ction of Light on Bacillus anthracis. 



41 



equally divided between woods and pastures. It seems likely that 

 the bright colours (often yellow) of the hymenopbores standing 

 upright among the blades of grass are of importance in this genus, 

 but the matter requires looking into. 



Uredineas are all orange to orange-brown, and remarkably brilliant 

 and well screened. Moreover, we have information as to the optical 

 properties of their colouring matters, &c, as already stated.* It is 

 surely a significant fact that these briglit orange Fungi are especially 

 leaf parasites, exposed to the full sunlight, direct or reflected, during 

 their whole course of spore formation, &c. 



Ustilaginece are all dark spored ; they look black in the mass, but 

 the colour is oftener a warm brown, and seems admirably adapted to 

 their habits. The conidial forms are developed in shade on the 

 ground. 



Ascomycetes require more examination as regards the colours of the 

 spores, but it is well known that many asco-spores are dark-coloured 

 or tawny, and the Nectrias and Pezizas show how thoroughly well 

 screened the developing asci are. 



The reds of the- Nectrias have been examined by Bachmann and 

 Zopf ; these colours may well be correlated with the exposure of the 

 perithecia and conidia in winter. 



The dark colours of the Sphceiacece and their allies are also probably 

 of use as screens, and the similar coatings to Sclerotia, which con- 

 tain large stores of reserves, may also be mentioned. 



There are certainly many more cases which seem to be explained by 

 the hypothesis ; but I will now turn to a few difficulties. 



I suppose the yellow stroma of Bpichloe sufficiently shields the 

 asco-spores in the sunken perithecia, but it seems difficult to explain 

 the purple stroma of the allied genus Claviceps ; nor can I explain 

 some other cases of purples and blues as yet. 



Bachmann, whose work on the spectroscopic analysis of fungus 

 pigments I have already referred to, investigated these colours from 

 all parts of the plants concerned, and dealt with spores only, or 

 almost only, in the case of Zfredinece. Consequently I cannot utilise 

 his other results directly. At the same time it is worthy of notice, 

 that on looking over Bachmann's forty-two absorption-spectra of 

 colours of Fungi — including reds, violets, and orange hues — it is 

 significant that the extreme blue-violet, from the line G onwards, is 

 cut out entirely in all but two cases, in each of which the absorp- 

 tion begins on the violet side of Or. 



The extreme red, near the line A, seems always to be absorbed 

 also. 



Then we find differences. The red pigments of Russula, Gladonia, 



* Kathay thought the colours of Uredinece attracted insects ('Denkschr. d. K. 

 Akad. d. Wiss., Wien,' 1882, vol. 46). 



