Fungi on Culture Media. 115 
fact that Fusarium stales under conditions in which Sphaeropsis does not; 
this is in accordance with a large body of evidence which indicates that 
Fusarium is a fungus with stronger staling tendencies than Sphaeropsis. 
The amount of staling shown can also in certain cases be modified by 
a slight alteration of the conditions under which the experiment is set up. 
Fig. 6 is an example of this. Both graphs represent the growth of 
Sphaeropsis on shallow layers of potato 
agar, the difference being that in 
the one case (the lower graph) growth 
took place in closed Petri dishes, in 
the other the Petri dishes were placed 
with the lids off in large five-litre 
containers. The difference was simply 
one of the volume of atmosphere in 
direct communication with the grow¬ 
ing fungus, and it was sufficient to 
influence distinctly the incidence of 
staling. This type of experiment has 
been repeated many times under varying conditions with Sphaeropsis on 
potato agar culture, and the above result has been confirmed in every case. 
In the case of Fusarium , the same result is obtained, but as a rule to a less 
marked degree. 
The foregoing result indicates that we are dealing here with an effect 
produced by differences in the conditions of gaseous exchange in the two 
cases. The two main possibilities which suggest themselves are (1) that in 
the closed Petri dishes limitation of oxygen supply is the cause, (2) that 
a gas which retards growth tends to accumulate in the closed Petri dishes. 
Table II, which is a fuller record of the experiments from which Fig. 6 
was taken, indicates which of the above alternatives is the likely one. The 
figures in the table represent the total diameter (in cm.). 
Table II. 
Total growth of Sphaeropsis on Potato agar , T. 14-15 0 : 
f 
2nd 
j\th 
$th 
_ 
6 th 
*jth 
Sth 
... ^ 
9 th 
day. 
day. 
day. 
day. 
day. 
day. 
day. 
Closed P. D.’s; deep 
1.65 
3.98 
4-97 
6-07 
7-°9 
8-o 
8.52 
,, ,, ..shallow 
1.50 
3 - 7 r > 
4.65 
5-40 
5- 8 5 
6-io 
6-20 
Open ,, deep 
1.65 
4-12 
5.28 
6.56 
7 - 7 1 
8.74 
9.6 
„ „ shallow 
1-64 
4-10 
5- 2 5 
6-54 
7.62 
8-55 
9-33 
From this table it is seen that the effect of opening the Petri dishes is 
to increase the growth both on the deep and shallow plates, but especially 
on the latter. The shallow closed plates show very strong staling, the 
corresponding deep plates show definite staling at about the eighth day, 
while the cultures in the open plates only show slight staling at the end of 
the experiment, so little in fact that the deep and shallow plates are still 
Fig. 6. Sphaeropsis malorum on potato agar. 
