276 Broivn . — On the Germination and Growth of 
effect just described is more markedly shown by cultures on potato agar, 
though it is also seen on other media. Also it is met with in the case of 
other fungi which show marked staling on potato agar. Such fungi are, 
in addition to Fits avium, Sphaeropsis malorum and more markedly Colleto - 
trichum Lindemuthianum. The effect is not seen with fungi such as 
Alternaria grossulariae , Botrytis cinerea , &c., which show no such marked 
development of alkaline reaction on potato medium. 
2. On comparing different fungi with each other in respect of the 
amount of retardation produced by a given concentration of carbon dioxide, 
it was seen that some are more susceptible than others. One could thus 
arrange the various fungi in a series of diminishing susceptibility, and this 
series was roughly the same as that given on p. 283, which is based on the 
concentration of carbon dioxide necessary to inhibit spore germination. 
In constructing such a table on this principle, one is limited to a consideration 
of the early phases of growth, as the staling effect by and by comes in as 
an important disturbing factor. However, it is quite possible to show that 
at ordinary temperatures a given concentration of carbon dioxide exerts 
a greater retarding effect on Botrytis cinerea than on Sphaeropsis malorum , 
at all stages of growth on all the media tested. When, on the other hand, 
the experiment is repeated at 5 0 the reverse is found to be the case. 
Whereas Botrytis colonies grow at 5 0 in 20 per cent. C 0 2 , Sphaeropsis 
colonies under these conditions are practically inhibited. The explanation 
of this is probably to be found in the different temperature minima of the 
two fungi. The minimum for Botrytis is very near o° 5 and that for 
Sphaeropsis was shown to lie between 3 0 and 5 0 . The greater effectiveness 
of 20 per cent. C 0 2 in the case of the latter fungus is probably correlated 
with the fact that the experimental temperature is approaching very close 
to the minimum for the fungus. It is reasonable to suppose that within 
a few degrees of the minimum temperature a moderate concentration of 
carbon dioxide is effective in producing not merely retardation but total 
inhibition of growth. Thus the region of total inhibition by 20 per cent. 
C 0 2 is already reached at 5 0 in the case of Sphaeropsis, whereas a lower 
temperature has to be sought in the case of Botrytis. 
3. The amount of retardation of growth at a low temperature 
produced by a given concentration of carbon dioxide is different according 
as the colonies have been grown throughout at the low temperature or 
were started at a higher temperature. The quantitative effect produced 
here appears to depend considerably on the particular medium used. The 
following table refers to Botrytis cinerea inoculations on apple gelatine : 
(a) B. cinerea grown throughout at 5 0 . 
Diameter of growth after 23 days : 
Air , io°/ 0 C 0 2 . 20°/ o C0 2 . 
7.6(100) 3-35 ( 44 ) 0-85(11) 
