Fungi at various Temperatures , &c. 265 
probably of no practical importance, seeing that such a density of suspension 
as that represented by m is very much greater than any that would ever be 
met with in practice. For densities such as m/100 and less, this mass 
effect arising from the spores becomes less pronounced, and for the dilute 
suspensions which are typically used for germination and infection studies 
its effect is more or less negligible. 
In the foregoing experiments the concentration of oxygen was not kept 
absolutely constant in the different cases. Taking ordinary air as containing 
20 per cent, oxygen, the concentration of the latter in the container set 
up with 10 per cent. C 0 2 would be approximately 18 per cent. (20 per cent, 
x 90 ■— 100), and the corresponding oxygen concentrations for the experi- 
ments with 20 per cent, and 30 per cent. C 0 2 would be 16 per cent, and 
14 per cent, respectively. The following tables show that such variations 
of oxygen concentration are of negligible importance, and, more generally,, 
that the germination of Botrytis spores is independent of oxygen con- 
centration over a wide range. 
The various oxygen concentrations were made up by suitable admixture 
of atmospheric air and of oxygen or nitrogen from cylinders. The method 
of procedure was that employed for the carbon dioxide atmospheres. The 
symbols used in the following table are the same as in the preceding tables. 
Table III. 
Effect of Oxygen on Germination of Botrytis Spores . 
A. Effect of Increased Oxygen. 
% Oxygen. % Germination of spores in 
water. 
m/100. 
m/10. 
m. 
21 
75 
59 
3 ° 
30 
65 
47 
30 
5 ° 
45 
23 
0 
80 
45 
2 5 
0 
B. Effect of Decreased Oxygen. 
% Oxygen. Spores in water. 
Spores 
in T.E. 7 10. 
m/100, m/10. 
m. 
m/100. 
m/10. m. 
21 
15 3 
0 
83 
79 20 
5 
20 4 
0 
84 
70 20 
1 
0 0 
0 
20 
— 5 
It will be observed that the amount of germination in a given time 
diminishes with increasing concentration of oxygen, but only very slowly, 
so that even in water quite a good germination results in 80 per cent, 
oxygen. Again, as the oxygen pressure is diminished, no appreciable effect 
is shown until very low concentrations of oxygen ( c . 1 per cent.) are 
reached. These results were in accordance with anticipation based on the 
statements of previous workers already cited, and they showed that, as far 
as the present investigation was concerned, the effects of changes of oxygen 
pressure on spore germination could be ignored. In subsequent experi- 
ments dealing with the rate of growth of fungal colonies this point was 
U 2 
