28 i 
Fungi at various Temperatures , <5jV. 
of growth already made, and to the diluteness of spore suspension (all 
within limits). All the experimental results obtained will then fall under 
the following general rule, viz. that the carbon dioxide retarding factor has 
greatest effect when the energy of growth is small. This general statement 
will cover all the experimental results obtained for the retarding effect of 
carbon dioxide on growth at different temperatures, in different concentra- 
tions of nutrient, and at different stages of growth. It will also include 
certain results obtained by comparing the retarding effect of carbon dioxide 
on the growth of some fungi on living fruit with that on artificial medium. 
On referring to Table IX, it will be seen that at 15 0 a given concentration 
of carbon dioxide more effectively retards the parasitic attack of Botrytis 
cinerea on apple than is the case with attack by Monilia cinerea . On 
artificial media both fungi were seen to be about equally sensitive to the 
action of the fungus. Now Botrytis is a weaker parasite on apple than is 
Monilia , and though a large number of factors may play a part in producing 
this result, one can state generally that living apple tissue is a poorer 
nutrient for Botrytis than for Monilia. Thus the figures shown in Table IX 
can be brought into line with the general rule that the retarding effect of 
carbon dioxide is greater the poorer the nutritive value of the substrate for 
the particular fungus. Some of the results of Brooks and Cooley already 
cited will also be seen to be interpretable along the lines of the general rule 
here put forward. 
The following practical considerations which arise from the foregoing 
work may now be briefly described : 
1. Within the limits of carbon dioxide concentration admissible in 
practice, carbon dioxide is not so important a factor in reducing the amount 
of fungal growth as is temperature. At ordinary temperatures a con- 
centration of carbon dioxide as great as 20 per cent, is not so effective in 
controlling fungal growth as is a drop of io° without carbon dioxide. 
2. The efficiency of the carbon dioxide treatment depends on the 
amount of nutrient available for the fungus. A concentration of carbon 
dioxide of 10-20 per cent, would give a good effect on spores devoid of 
nutrient and a much less effect on spores which had free access to nutrient, 
and less still when attack had already started. The nutritive conditions 
obtaining on the surface of stored fruit will obviously depend on a number 
of factors — the particular kind of fruit, the soundness of the fruit, &c. 
Where the fruit is injured in any way, nutrient will always be available to 
any fungal spores which happen to be present, but even under the best 
conditions of storage a certain amount of nutrient will always be available 
to fungal spores (at least in the case of apple), as it has been shown in 
unpublished work of the writer that certain volatile products of the apple 
have a very distinct accelerating effect on spore germination. The food 
available to the fungus is therefore never negligible. As regards the effect 
