Fungi on Culture Media. 127 
General Discussion. 
In the earlier portion of this paper the growth-rate curves of a number 
of fungi were given, from which it appeared that after an initial period of 
slow growth the rate of growth reached a maximum at which it remained 
steady, or from which it subsequently declined. This effect of reduced rate 
of growth is obviously a case of staling of the growing margin of the 
mycelium by the products formed within its mass, a conclusion with which 
all the results of the present paper are in agreement. These products 
either diffuse outwards beyond the limits of the growing margin or, as in 
the case of ammonia, pass into the atmosphere of the culture and from 
there are absorbed by the cultural medium. The result of this is that the 
portion of the medium on which the growing margin of the colony is enter¬ 
ing becomes less suitable day by day for the growth of the fungus, and thus 
staling of the margin begins. 
In any case where staling does not occur (e. g. Botrytis growing on 
potato agar), one must assume that the fungus produces no appreciable 
amount of staling substances or that it is very insensitive to their presence, 
whereas in the case of a staling culture, e. g. Fusarium on potato agar, the 
assumption must be either that the fungus produces large quantities of 
staling substances or that it is highly sensitive to their action. Now, though 
the ultimate proof must be a chemical one, there is little doubt that it is the 
former alternative that rules. Botrytis is a non-staling form simply because 
it produces relatively little staling substance. In both cases the dominant 
feature of the staling process from the chemical point of view is the develop¬ 
ment of an alkaline reaction in the potato medium, and this is very much 
more pronounced with Fusarium than with Botrytis. Again, it is easy to 
show that the sensitiveness of Botrytis to alkalinity in the medium is much 
greater than that of Fusarium. (See Table V.) 
The views here put forward are strikingly confirmed by a comparison 
of the behaviour of colonies of the two organisms growing on the same 
plate, as compared with controls in which each is growing alone. *The 
growth of Fusarium in presence or in absence of Botrytis is very much the 
same : that of Botrytis is obviously affected by the presence of the Fusarium . 
On such a medium as potato agar where ammonia is evolved by the 
Fusarium , the growth of the Botrytis colony is reduced and finally stopped 
in all directions. On a medium from which ammonia is not evolved, the 
Botrytis colony is strongly staled on the side next the Fusarium, so that it 
appears excentric, while the Fusarium colony will preserve its circular out¬ 
line much longer. 
The only view which will thus meet the experimental facts is that 
Botrytis tends to be a fungus of unlimited growth simply because its capacity 
to form staling products is small, whereas Fusarium , though it is compara- 
