210 Mr. Hall, Dr. Miller, and Mr. Gimingham. . [ Dec. 19, 
Mucor, Trichoderma, and Acrostalagmus have also been observed, but the 
description of the fungus flora present in the soil of these plots will be 
given elsewhere. ‘The essential point is that both the dominant species, 
Penicillium and the Mucor, and several of the others examined, when grown 
into a nutrient medium containing a carbohydrate and an ammonium salt, 
draw the nitrogen they require from the ammonia and leave the acid ina 
free state. This production of acid by Penicillium growing in a medium 
containing an ammonium salt has already been observed.* The following 
experiments will serve to illustrate the extent to which the action takes 
place :— 
Experiments with Mucor sp.?—Flasks were made up with 60 c.c. of a 
nutrient solution containing varying amounts of ammonium chloride and 
cane-sugar as under; the flasks were incubated at 21° C., and the acidity 
determined after 34 days, with the results set out in the last columns :-— 
Gain of acidity as Percentage of ammonium. 
NEC Ranessugar. c.c. 2/10 acid. chloride converted. 
gramme. grammes. 
Axl 0° 1-2 11 °6 13 ‘9 
A2 0°6 0°6 8-0 V2 
Bl 0°3 1:2 8°1 14°5 
B2 0°3 0°6 6°9 12 3 
C1 0°06 1°2 ga 81-7 
C2 0 ‘06 0°6 8°5 75 °0 
The highest acidity observed at the end was equivalent to about a 1/50 
solution of free acid. 
When a small quantity of asparagine was also added to the nutrient 
solutions the increase of acidity was negligible; the organism satisfied its 
requirements for nitrogen from the asparagine in preference to the ammonium 
chloride, which, in consequence, remained undecomposed. 
Experiments with Penicillium.—-One of the forms of Penicillium was 
seeded into a solution containing 1 per cent. glucose, 0:25 per cent. ammonium 
chloride, and the usual nutrient salts. Growth was fairly vigorous and was 
stopped after 14 days, when the yellow solution was filtered off and tested 
for acidity and ammonia, showing the following results for 100 c.c. of the 
original solution :— 
Acidity Nitrogen Ammonia removed. 
as c.c, 2/10. as ammonia. 
Check 0 0 063 
A 5°5 0 059 0 004 = 2°8 c.e, n/10 acid 
B 52 0 058 0005 = 3°5 
bP 
The acidity in this case has been increased, though not to the extent 
* Kohn and Czapek, ‘ Beitr. Chem. Physiol. Path.,’ 1906, vol. 8, p. 302. 
