28 The Philippine Journal of Science mz 
their own disappearance; by the competition of the later plants 
of a succession when the substratum is prepared for them. 
They also show that variations in the moisture content of the 
substratum are not responsible for the succession. 
The order in which the fungi become visible in the unsterilized 
cultures would appear to be due to their various rates of growth 
and not to some having started before the others. The mucors 
on sterilized media grow rapidly and fruit in three days. 
Oospora grows much more slowly and so does not become visible 
until after the molds. The difference in the rates of growth of 
these fungi on agar in test tubes is very striking. In three days 
the mucors fill the tubes while in the same time Oospora makes 
only a slight growth. The hyphae of the Coprini grow rapidly 
from the first on sterilized dung, while they can be distinguished 
only with difficulty in unsterilized cultures. In either case it 
takes them about ten days to fruit. It will thus be seen that 
their presence in unsterilized cultures would not be recognized 
until they had fruited or, in other words, not for ten days. 
The difference in the growths obtained on sterilized and 
unsterilized dung would seem to show that the disappearance of 
the mucors and Oospora in the latter case was due to micro- 
organisms in the substratum. Probably the chief effect of steril- 
izing is the killing of all of the organisms. We have seen that 
the changes in the moisture content of the dung are insignificant, 
and it is not likely that the food supply is altered sufficiently to 
explain the results. A great variety of microorganisms occur in 
the dung in large numbers. These would certainly compete with 
the fungi for food and oxygen and in all probability would also 
excrete toxic substances which would be detrimental to them. 
If these microorganisms are allowed to remain in the dung for 
ten days it will not support the Mucors even when inoculated 
with them. If now it is sterilized with either. steam, chloroform 
or formalin, which three methods were tried, it will again 
support a vigorous growth of fungi. The steam might cause 
the volatilization of toxic organic compounds but it is not likely 
that the latter would be destroyed by both chloroform and 
formalin. From this it would seem that the removal of the 
competition of the microorganisms is sufficient to prevent the. 
early disappearance of the molds, but it is also quite probable 
that the microorganisms excrete substances which are harmful 
to the fungi although definite proof of this is lacking. 
From the foregoing it is evident that the order in which the 
fungi appear in unsterilized cultures is due to their different 
