2jS 
Brown . — On the Germination and Growth of 
A comparison of the figures obtained at the two temperatures of the 
experiment again shows that the relative retarding effect of a given con- 
centration of carbon dioxide is accentuated by lowering the temperature. 
The comparatively high degree of retardation produced by carbon dioxide 
on the rate of Botrytis attack as compared with that of Monilia would seem 
to be correlated with the less vigorous parasitic action of the former on 
apple. 
Discussion. 
As the main part of the foregoing experimental work deals with the 
rate of increase in diameter of fungal colonies, a brief discussion of the 
method of measurement adopted is necessary here, though a fuller criticism 
is reserved for a future occasion. 
For the present investigation (as for many others of a physiological 
nature) the really important quantity to be determined in connexion with 
fungal growth is the amount of work done, i. e. the amount of chemical 
transformation carried out. This quantity, which would be very difficult 
to determine directly, is in all probability closely related to the amount of 
growth made by the fungus. There is thus a rough proportionality between 
the amount of chemical transformation effected by the fungus and the 
amount of fungal mycelium. The question now arises as to the relation 
between the amount of mycelium in a fungal colony and the diameter of the 
latter. As between different media, or even different concentrations of the 
same medium, there is no relation between the amount of mycelial growth and 
the diameter. On some media a given fungus may produce a dense weft 
with slowly advancing margin, and on others a thin colony with rapidly increas- 
ing diameter. In such a case measurement of the diameter is of no value in 
determining the amount of growth made by the fungus in the different cases. 
When, however, comparisons are made between growths under different 
conditions on the same medium, definite conclusions as to the amount of 
mycelium can be drawn from a measurement of the diameter of the colony. 
With any particular medium, the type of growth produced by the same 
fungus is very similar under the different conditions of experiment, whether 
in air or in concentrations of carbon dioxide, or whether at laboratory 
temperature or in cold store. With fungal colonies growing on the same 
medium, the diameter of the colony is a measure of the amount of growth 
in the sense that a greater diameter represents a greater amount of 
mycelium than does a smaller diameter, and conversely. 
The exact relation between diameter of colony and amount of mycelium 
is not certain, and almost certainly varies with the age of the colony. If 
the colony grew spherically on the medium (or on the fruit) the amount of 
mycelium would be more or less proportional to the cube of the diameter, 
but, as is noted by Brooks and Cooley (4), the colony always spreads more 
