123 
Fungi on Culture Media. 
<3 
comparable amount of drying of the medium before inoculation has no 
such effect. Obviously this result can only apply within certain limits. 
Though this line of experiment was not followed out farther, the sugges¬ 
tion seemed to be either that some transpiration effect was coming into 
play or desiccation of the growing cultures led to a concentration of the 
staling substances, especially, perhaps, on the surface-layer of the medium. 
It was obvious from these control experiments that it was necessary, 
in using various solutions as gas absorbents, to have the solutions weak 
in order to avoid any effects due to drying of the cultures. Hence i per 
cent, sulphuric acid and i per cent, caustic soda were used. 
The dependence of staling upon carbon dioxide and ammonia was 
best brought out by experiments such as those recorded in Table X. 
Table X. 
(a) Growth of Sphaeropsis on potato agar in open Petri dishes in 5-litre containers: 
Control. Growth in open P. d.’s in container over 
(In closed P. d.’s .) 
S.r 
100 c.c. 
H 2 0 (air). 
8.7 
100 c.c. 
1 % NaOH. 
7-7 
100 c.c. HoO 
(5 % C 0 2 ). 
9.4 
(b) Growth of Sphaeropsis on potato agar in closed Petri dishes with watch-glasses containing 
a few cubic centimetres of various liquids inside : 
P. d.’s with 
nothing inside. 
5-69 
P. d. ’s zvith 
water. 
5* 8 7 
P. d.’s with 
1 % NaOH. 
5-77 
P. d.’s zvith 
I % h 2 so 4 . 
6.52 • 
Summarizing the results of all the experiments made with potato agar 
as medium on the lines indicated in Table X, one can draw the following 
general conclusions : 
Experiments in containers .—The amounts of growth over water and 
over 1 per cent, sulphuric acid are not appreciably different, as the stal¬ 
ing factor is very much reduced by simple dilution due to the large air¬ 
space introduced. Both are distinctly greater than the growth in closed 
Petri dishes and in the open Petri dishes over soda. Of the last two, 
one was sometimes the greater, sometimes the other, and no general rule 
was found. The growth in the containers over water in 5 per cent, carbon 
dioxide was always the best. 
Experiments in closed Petri dishes. —Here the small amount of water 
introduced is of no value as it rapidly becomes alkaline: the improvement 
due to the introduction of sulphuric acid is here rendered distinct. 
Experiments similar to those described for Sphaeropsis were carried out 
at the same time for Fusarium. The results here were of the same type, 
and all the results established for Sphaeropsis found a parallel in the 
experiments with Fusarium. The results were, however, somewhat dif¬ 
ferent in degree. The most striking difference lay in the fact that while 
