84 CULTURAL STUDIES OF SPECIES OF PENICILLIUM. 



incapable of assimilating nitrogen from the sodium nitrate of this 

 solution. Four more forms — P. brevicaule and its closely related 

 varieties, and P. roseum Link — reached normal appearance slowly. 

 Other cultures indicate that these forms assimilate nitrogen in this 

 form less readily than in organic combinations. This medium con- 

 taining cane sugar in amounts as great as 20 per cent proved well 

 adapted for all other species tried. The medium as used was neutral 

 or slightly alkaline in reaction. Thirty-three of the forms inoculated 

 into it produced pronounced acid reactions to litmus in a few days, i. e., 

 were able to ferment this form of sugar. In prolonged culture with 

 smaller amounts of sugar, some of these forms finally reduced the 

 acidity and even brought about an alkaline reaction again; others 

 remained acid as long as observed. Twelve forms failed to produce 

 acidity. This number includes the four forms in which growth was 

 delayed and P. italicum, P. luteum,, P. jiurpurogenum, P. roqueforti, 

 and P. duclauxi. 



In cultures at a concentration of 60 per cent cane sugar, five forms 

 produced typical colonies at once; six others slowly reached normal 

 proportions ; a few more grew fairly well ; but fully half the species tried 

 produced germination with but little further growth. Water in 

 amount approximately to reduce the concentration to 35 per cent was 

 added to the cultures that failed to produce normal colonies, and this 

 was followed by the prompt recovery of several species which quickly 

 reached normal development. Critical examination of the data 

 obtained showed that closely related types responded in exactly the 

 same manner to changed percentages of cane sugar. As a means of 

 separating closely related forms, further determination seemed fruit- 

 less. Exact determination of the maximum percentages of cane 

 sugar tolerated by particular species has not been completed. The 

 inhibition is not a stoppage of all development at a definite critical 

 concentration, but rather a gradual reduction of activities with the 

 increasing concentration of the medium. Specific maxima and 

 minima are therefore almost impossible to define. All determina- 

 tions would therefore rest upon the judgment of the observer rather 

 than upon fixed standards. 



Lactose (Tables 4 and 5). — Lactose was added to Dox's fluid in 

 percentages up to 10 per cent. Prompt and normal development was 

 determined in eight forms ; nine more forms reached typical appearance 

 more slowly. Only twelve of these produced definite acid reactions to 

 litmus. Among the forms included in the seventeen, four groups of 

 closely related organisms were found, namely, the camemberti group, 

 Nos. 5, 6, 39 ; the common green group, Nos. 22, 23, 40 ; the chrysogenum 

 group, Nos. 25, 26, 35, and 44; and the brevicaule group, Nos. 2, 3, 

 and 4. With lactose as with cane sugar closely related forms give 



