55 ^ Balls . — Temperalure and Growth. 
for a cell under standard conditions, belong to a different category from 
those environmental factors which — the power to grow being granted — 
determine the relative amounts of that growth under varying external 
conditions. 
It is hardly necessary to point out that the experimental and analytical 
methods employed are based on Blackman’s ‘ Theory of Limiting Factors’. 
In ‘ Optima and Limiting Factors 1 he points out that ‘ the way of those who 
set out to evaluate exactly the effects of changes in a single factor upon 
a multi-conditioned metabolic process is hard, and especially so when the 
process is being pushed towards the upper limits of its activity’. 
Preliminary Work 
In my first publication 2 concerning the Sore-shin fungus it was stated 
that the growth of the fungus was soon inhibited at 34° C. on agar media, 
and that this inhibition corresponded to the results obtained by raising the 
temperature of an infected cotton seedling. The wide interval between the 
‘ inhibition temperature ’ and the death-point led me to examine the matter 
further, in mass cultures and in hanging drops. The apparatus in common 
use for the latter purpose was proved to be untrustworthy, and all the 
results obtained with it have been omitted from this account, being super- 
seded by the later work here given. 
Solid Media. The results were at first erratic when the cultures in 
agar streak tubes were repeated ; growth might continue freely over the 
surface of the jelly, or it might cease after an hour or two, as in the first ex- 
periments. The cause of this irregularity was found in the texture of the 
jelly, the former being the case on soft agar, and the latter on agar which 
had become dry and tough through storage in the dry air of the laboratory. 
Growth on soft agar at 34 0 C. was not normal ; it was marked by 
a tendency to form aerial hyphae, which grew rather more rapidly than 
those on the agar, so that the marginal extension of the mycelial disk was 
carried on by the return of these aerial hyphae to the surface, slightly 
in advance of those which already formed the edge. 
These facts accorded with the expectations based on the hypothesis of 
poisonous excreta accumulating in the jelly and thus inhibiting the growth 
of the hyphae, entirely or partly. Renewal of growth at a low temperature 
would be due to the removal of the excreta, either by decomposition or by 
diffusion. 
Liquid media should not exhibit this cessation of growth until several 
days had elapsed, owing to the free diffusion of the excreta away from the 
vicinity of the hyphae. 
Liquid Media. Cultures stored at 20° C. develop mycelium with 
a smooth appearance, the hyphae branching occasionally and being almost 
1 Annals of Botany, April 1905. 2 Khech Agric. Soc. Year Book, 1905. 
