OBSERVATION AND DESCRIPTION OF PENICILLIA 29 



substratum, groA^Ti at a definite temperature, fall fairly consistently 

 within a narrow range of tints and shades of some particular mixture of 

 colors, as for example yellow and green, blue and green, red and orange, 

 orange and yellow, etc. The culture medium used, however, must be the 

 first item specified if the color ranges which are cited are to have real 

 value. 



The range of colony colors within the genus Penicillium is quite wide. 

 Included are a few forms that are white and others which show mixtures of 

 orange and yellow with admixtures of red. The great majority of forms, 

 hoAvever, develop colors in yellow-greens, greens, and blue-greens during 

 their fruiting periods, thus accounting for the common lay reference to 

 them as "green mold" or "blue mold." Many of these PeniciUia lose all 

 of their green color in age and assume various shades of yellowish brown, 

 reddish brown, olive gray to almost fuscous. In none of the typical 

 PeniciUia, however, are the above colors accompanied by the heavy, 

 brouTi cell walls characteristic of the Dematiaceae. 



COLOR IN THE MYCELIUM AND SUBSTRATUM 



The aerial mycelium in Penicillium is nearly always colorless. Areas 

 of yellow and red h^'phae commonly appear in the Biverticillata-SjTnme- 

 trica section, and occasionally elsewhere, but when subjected to micro- 

 scopic examination the coloring substance is found to be largely deposited 

 as granules on the surface of the cell wall rather than within the cell itself. 



The submerged mycelium of various species and groups, on the other 

 hand, shows a series of yellow, orange, red, brown, lilac, or hyacinth 

 colors with occasional green and even black areas appearing. Such colors 

 are best seen from below and are routinely designated as color of reverse, 

 or simply "reverse." 



Pigment production in the mycelium, even more than in conidial areas, 

 is influenced by changing the nutrient composition of the substratum. 

 Hence, it is always essential to specify the character and composition of the 

 substrate employed when citing any color as characteristic of the mycelium 

 of a particular strain, species, or series. 



Whereas contrasts in color may occur in some series, in the majority of 

 cases certain ranges of color are found to be correlated with fairly consistent 

 morphological characteristics. Within a given series a particular species 

 may be able to carry color production up to a certain point represented by 

 an identifiable tint or shade. Another related species, beginning at the 

 same point, may carry the process further, and a third species may carry it 

 still further. This is well illustrated in the Penicillium 'puryurogenum 

 series. 



The coloring matter present in the submerged mycelium may or may not 



