I 2 [ 
Fungi on Culture Media. 
culture. As potato extract is practically neutral, free ammonia appears 
sooner in cultures on potato gelatine. 
It now remains to show how far the ammonia given off by a fungus 
is responsible for slowing down the growth of the fungus itself, and also 
to demonstrate what part the carbon dioxide of respiration plays in the 
staling process. 
The general method of experiment was to compare the growth of 
a fungus on a given medium in closed Petri dishes with the simultaneous 
growth of the same fungus on the same medium in open Petri dishes. The 
latter were stacked in 5-litre glass containers with an air-space between 
each. In the bottom of the containers 100 c.c. of a liquid were placed, 
either water or 1 per cent, sulphuric acid or 1 per cent, caustic soda. 
The initial atmosphere was either ordinary air or air with its carbon dioxide 
content made up to 5 per cent. It was not possible to obtain incubator space 
for all the containers used, so all the experiments were carried out at 
laboratory temperature. As only the relative degree of staling in the 
cultures as differently set up was of importance, and as each one had the 
same temperature conditions, the experiments lost nothing in value on this 
account. 
Fig. 6 illustrates the fact that the growth of Sphaeropsis on potato 
agar is much improved by removing the lids of the Petri dishes and 
placing the latter in large containers ; in addition 100 c.c. water were 
placed in the bottom of each container. This experiment has been re¬ 
peated a large number of times and always with a distinct, positive result. 
The following series of figures is typical of the results obtained, and 
shows the magnitude of the effect produced. In all the experiments re¬ 
corded in the table the medium was potato agar, poured deep, with the 
exception of the ones marked shallow. These experiments were performed 
at all seasons of the year, and so laboratory temperature varied considerably 
from one to the other. There is thus no correspondence between the 
average growth per day in each experiment. Each figure represents the 
average of four cultures. 
Table VIII. 
Growth of Sphaeropsis. 
Duration of 
Experiment . 
Closed Petri 
Dishes. 
Open P. d.'s in 
Container over 
100 c.c. Water. 
7 
days 
7-45 
8-62 
5 
>> 
5-93 
6-04 
6 
yy 
5 - 5 6 . 
5*8 
10 
yy 
8.1 
8-7 
10 
„ (T. i7°C.) 
9 -2 7 
10.67 
10 
» (T. i 4 °C.) 
5*48 
6-45 
13 
\ deep 
8-40 
10.50 
\ shallow 
6-05 
9-45 
j deep 
5-05 
5*38 
U 
” \ shallow 
3.81 
4.40 
