[Vor. 8 
202 ANNALS OF THE MISSOURI BOTANICAL GARDEN 
of normal Czapek's solution. With the peptone and the beet 
decoction solutions, however, N/5 KOH has been used. In all 
of the media, namely, Czapek, peptone, beet decoction, and 
water (adjusted by HCl), N/5 HCl was favorable for varying 
the reactions on the acid side. 
Inasmuch as sugars generally react with acid and alkali when 
heated under pressure, the nutrient solutions and the acid and 
the alkali were sterilized separately. Thirty cc. of the nutrient 
solution together with the desired amount of water, the amount 
of which equals the difference between the total volume and the 
sum of the volumes of the nutrient solution and the acid or 
alkali to be added, as shown by fig. 1, were put into small flasks 
plugged with cotton, and sterilized. After cooling ,the cultures 
were removed to a culture room, and the definite amounts of 
sterile acid and alkali were added with sterile graduated pipettes. 
The final volume of each culture was 50 cc., and each case repre- 
sented a dilution of the constituents comparable with that in 
the original nutrient solution. The solutions were allowed to 
stand at least 24 hours in order to reach a state of equilibrium 
before H-ion determinations were made. A certain small amount 
of precipitate occurred upon the addition of alkali, the amount 
increasing with increase of added alkali. Mannite was sub- 
stituted for cane sugar, called for in the formula, in order that 
the same carbohydrate might be present in both the single and 
the full nutrient solutions, the plan being to make the experi- 
ments with the 2 types of media as comparable as possible. 
Peptone.—A 2 per cent bacto-peptone solution, prepared 
according to the titration curve of Karrer and Webb (720), was 
used in this investigation. The 2 per cent bacto-peptone solu- 
tion normally tests Pa 7.0, and the hydrogen-ion concentration 
was varied with N/5 HCl and N/5 KOH. The buffer action, 
it will be noticed, is relatively slight on the alkaline side, and is 
even less apparent in the range Py 5.0-7.0, the addition of a few 
tenths of a cubic centimeter of acid producing an almost vertical 
ascent in the titration curve. With increasing acidity above 
Px 5.0, however, buffer action is relatively strong. No pre- 
cipitation was evidenced in the alkaline cultures of this medium. 
