294 PHYSIOLOGY OF THE FUNGI 



larger fruit bodies of the fungi are entirely black, although this is a com- 

 mon color for perithecia, pycnidia, and spores. 



Among the nutritional factors which modify the production of pigments 

 by fungi in culture, the micro essential elements, the carbon and nitrogen 

 sources, the initial pH of the medium, and the temperature are important. 

 Perhaps the first of these factors to be studied was the effect of iron, cop- 

 per, zinc, and other micro elements upon the spore color of Aspergillus 

 niger. Copper seems to play an outstanding role in the production of 

 dark spores by this fungus (Mulder, 1939), but low concentrations of 

 other micro essential elements also affect spore color of this fungus. The 

 influence of iron, copper, and zinc on the pigmentation of mycelium and 

 spores, and the production of soluble pigments by certain species was 

 studied by Metz (1930). 



The investigation of the chemical structure of fungus pigments has 

 formed an essential part of a comprehensive study of the products of 

 fungus metabolism at the University of London. The citations in this 

 paragraph will give the reader entry into this excellent work. Many 

 fungi produce anthraquinone pigments. Helminthosporium gramineum 

 stores in its mycelium two pigments (helminthosporin and hydroxyisohel- 

 minthosporin), which may account for 30 per cent of the dry weight of 

 the mycelium. Helminthosporin is 2-methyl-4,5,8-trihydroxyanthra- 

 quinone (Charles et at., 1933). H. cynodontis and H. euchlaenae form 

 cynodontin, l,4,5,8-tetrahydroxy-2-methylanthraquinone, which is closely 

 related to helminthosporin (Raistrick et at., 1933). Some 12 anthra- 

 quinone pigments are produced by fungi (Howard and Raistrick, 1949). 

 Xanthone pigments are produced by H. ravenelUi and H. turcicum (Rai- 

 strick et at., 1936). The production of anthraquinone pigments is not 

 restricted to species of Helminthosporium, for Penicillium islandicum 

 synthesizes chrysophanic acid, 4,5-dihydroxy-2-methylanthraquinone 

 (Howard and Raistrick, 1950). In general, the production of these and 

 other pigments is modified by the cultural conditions used. The produc- 

 tion of helminthosporin by H. gramineum was increased when nitrate or 

 organic sources of nitrogen were used. Ammonium nitrogen was not 

 favorable for pigment production. More pigment was produced when 

 the initial pH was 8 than in more acid media. 



Many of the water-soluble pigments produced by fungi are indicators. 

 P. phoeniceum and P. ruhrum produce such an indicator pigment, phoe- 

 nicine (2,2'-dihydroxy-4,4'-ditoluquinone). The color changes of this 

 indicator are from yellow to red in the pH range of 1.8 to 3.4 and from 

 red to violet in the range 5.4 to 6.4. As much as 2 g. of this pigment is 

 produced by P. ruhrum per liter of medium (Curtin et al., 1940). 



The functions of fungus pigments are not well understood. It is 

 known that certain of these pigments are enzyme inhibitors. Others, like 



