Fungi 07 i Culture Media. 129 
Sphaeropsis. In the experiments recorded in this paper it was shown that 
the improvement of growth resulting from diminution of the ammonia 
factor was more marked in the case of Sphaeropsis than of Fusarium. In 
the latter case mere removal of ammonia did not very greatly improve 
growth, but raising of the carbon dioxide concentration in the atmosphere 
of the colony produced a very distinct effect. Thus we may say that in the 
case of Sphaeropsis the volatile alkali is more effective in causing staling 
than the fixed alkali, whereas with Fusarium the converse is true. 
It will be observed that the points brought forward in the present paper 
explain fully the unexpected results mentioned in the introduction. The 
fact that some fungi (e. g. Fusarium , Sphaeropsis ) show more growth after 
a time in a moderate concentratian of carbon dioxide than in air is correlated 
with the production of an alkaline staling reaction in the medium. Thus, 
though carbon dioxide at the concentrations employed (10 to 20 per cent.) 
cannot be looked upon in any other sense than as a retarder of growth, it 
produces the opposite effect in such cases in virtue of its neutralizing action 
on the staling products. With such fungi as F>otrytis cinerea , where pro¬ 
duction of alkali is very slight, the effect described does not appear. 
Summary. 
Curves of the rate of growth, as measured in terms of the diameter of 
the colony, are given for a number of fungi. The general feature of these 
curves is that in the early stages the rate of growth is small, and that it 
then rises to a maximum which may, or may not, be maintained. 
Fungi which keep up this limiting rate of growth are described as 
being of the non-staling type ; those in which the rate of growth falls off 
from the maximum, are described as being of the staling type. 
The growth of Sphaeropsis malorum and of Fusarium sp. 011 potato 
agar which is of the staling type is studied in detail, when it is found that 
the relative amount of staling can be modified by various modifications of 
the experimental conditions, by varying the depth of the medium, and in 
particular by the arrangements made for disposing of two volatile products 
of the metabolism of the fungus, carbon dioxide and ammonia. According 
as the one or the other is allowed to accumulate, a greater or less degree of 
staling will result. 
The amounts of ammonia formed in Sphaeropsis cultures on a number 
of media are determined. 
Correlations between staling and sporulation, and between staling and 
the phenomena of intermingling, are indicated. 
K 
