COMPARA I l\'i: CULTURAL DATA. 83 



\(. LR- \<. Ai: A> A SOI i:< K OF POOD. 



Tubes of I .5 percent agar-agar in distilled water were inoculated 

 with eighteen species of PenicUlium. Sixteen of these produced 

 growth. In all cases the colonies produced were very small, some 

 of them barely discernible to the naked eye. Not one of them was 

 distinctly colored by conidia] masses, but in ncarh even ease some 

 conidial fructifications were found. These cultures show that the 

 species tested were able to obtain from the medium sufficient nourish- 

 meiit for very slight growth. 



AGAR-AGAR AS A SOURCE <>F CARBON. 



Agar-agar is a carbohydrate and might serve as a source of carbon 

 if other nutrients were supplied. One and one-half per cent of agar 

 was therefore introduced into Mr. Dox's synthetic fluid, already con- 

 taining all essential elements except carbon. Thirty-seven races of 

 PeniciUium were inoculated into this medium, and nearly every 

 species produced some growth. Examined with the microscope, 

 conidial fructifications were found in nearly every case, but in no 

 case was the colony large enough or definite enough to affect the 

 observer's estimate of results if such growth were added to or sub- 

 tracted from the colonies upon nutrients really adapted to sustain 

 the species studied. Dox's stock solution, with or without the addi- 

 tion of agar, was in this way shown to be a safe medium for the study 

 of the metabolic reactions of these species to changed sources of 

 carbon. 



The possibility of error in the introduction of agar was shown in 

 the following manner: One and one-half per cent of agar was intro- 

 duced into Dux's fluid and 1.1 normal lactic acid added in quantity 

 to make the whole 0.5 per cent acid. The medium was then auto- 

 claved. After this treatment the agar refused to solidify. Tubes of 

 tins fluid were inoculated with nine different species of Penicillin m. 

 All except P. breoicauL grew well and produced colonies recognizable 

 by their cultural characters. In introducing agar in such work it is 

 therefore accessary to guard against the introduction of acid before 

 dissolving the agar, since this changes the agar itself into other car- 

 bohydrates assimilable by fungi. Although parallel cultures were 

 commonly made with agar, the studies of metabolism recorded in this 

 paper were made in t nbe culture of the fluid nutrients only, to avoid 

 possibilit ies of error. 



VA1MOI s SOURCES OP CARBON. 



Cane sugar ( Tables ', and 5). Cane sugar was added to Dox's fluid 

 in the following percentages: 1 ..>, :;, 10, 20, 60, and 75. Of the spe- 

 cies used, but one — P. digitatum of Saccardo failed to grow typ- 

 ically. This, together with other work, indicates that this species is 



