122 
Journal of Mycology 
[Vol. 11 
difficulties are special cases and do not destroy the significance 
of the definite conduct of very many species. The value of other 
indicators has not been tested sufficiently to report results. Very 
few of the species tested so far, carry the medium to the alkaline 
side of Phenolphthalein, though several of the more strongly 
alkaline forms have done this. 
4. Secretions. 
Pigment production.— Some species produce pigments which 
are secreted, or perhaps better, excreted, into the substratum. 
Among the species of Penicillium studied at least two produce 
bright yellow pigment in considerable quantity. Several more 
at times exhibit a trace of this ability. Pigment production is 
dependent apparently upon the substratum. Neither of these 
species produce any color within potato agar but both will rap¬ 
idly turn a tube of milk yellow or cause large patches of yellow 
on bread, or potato plugs. This yellow pigment is soluble in 
alcohol. The whole question of pigments is, however, so imper¬ 
fectly known that its diagnostic value is very doubtful except in 
a few cases. 
II. The Colony Itself. 
Confronted with the necessity of being able to distinguish 
certain species, I next turned to the colonies and sought for 
characters which might be of value. Not to review failures cer¬ 
tain points have proved to be fairly reliable. Approximate uni¬ 
formity of media must be kept in mind, but the ordinary differ¬ 
ences between successive lots of gelatine or agar upon the same 
formula do not seem to disturb these relations in the species I 
have studied. I am informed by Dr. Haven Metcalf of Clemson 
College that the slightest changes in the medium do produce 
striking morphological changes in certain species of Frusarium. 
1. Color. 
The color and color-changes of colonies though difficult to 
describe must be observed and recorded for the entire growing 
period. In spite of the haziness of nomenclature in greens, blue 
greens, greys and browns, general distinctions can be made and 
are fairly reliable. Improvement in color charts would aid mat¬ 
ters greatly. Milburn has recently shown that changes in acidity 
of media in certain cases cause radical changes in the color of 
spores, and similarly variations in illumination and osmotic 
pressure affect the pigments in the spores of Hypocrea. Although 
my experiments with Penicillium have not yet produced such 
results this observation has been made upon P. glaucum by Dr. 
O. Stoll in a recent paper. This makes thorough knowledge and 
statement of conditions very necessary to uniformity of results. 
