758 
Journal of Agricultural Research 
Vol. V, No. 16 
of from 1/25 to 1/5 c. c. of hydrogen peroxid (3 per cent) would produce a 
few pycnidia with darkened cultures. In the stronger concentrations the 
mycelium was completely enveloped with a froth. After the first stimu¬ 
lation the cultures produced no further pycnidia. It must be said that 
in no case were pycnidia produced in amounts equal to those under 
light conditions. At best the use of hydrogen peroxid is a very harsh 
method. 
With young cultures or with very old cultures the hydrogen peroxid 
was ineffective. In these its behavior is like that of light. 
Other chemicals known to be strong oxidizing agents were employed. 
It may be said that nearly all gave positive results at extremely weak 
dilutions, provided that the mycelium used was in proper condition. 
Mycelium which would produce pycnidia by an hour’s exposure to light 
gave good results with the oxidizing agents. 
Another factor was doubtless responsible for the inequality of pyc- 
nidium formation in these experiments. All the chemicals used are 
toxic to the mycelium. In the concentrations used, these poisoned the 
cultures and certainly affected the reactions. 
Table XXX summarizes the successful trials. 
Table XXX .—Effect of change of intensity of a factor: Use of various chemicals 
Chemical and concentration. 
Corn broth. 
Synthetic. 
Pea. 
Nitric acid (HN 0 3 ), M/500_f.. 
+ 
4 
4 
Sulphuric acid (H 2 S 0 4 ), M/500. 
4 
4 
— 
Sulphuric acid (H 2 S 0 4 ), M/500,-|- potassium dichro¬ 
mate (K 2 0 r 2 O 7 ), M/500... 
4 
4 
_ 
Potassium permanganate (K^Mn 2 0 7 ), M/500. 
— 
— 
— 
Ferric chlorid (FeCl 3 ), 1 drop of M/5. 
4 - 
4 
— 
Zinc sulphate (ZnS 0 4 ), M/500. 
— 
— 
— 
GENERAL DISCUSSION 
The work reported in this paper has given more or less of a definition 
of the environment in which Plenodomus fuscomaculans can live and 
reproduce. We now know the bare essentials for growth—the base level 
of existence—since we know the minima of the various formal condi¬ 
tions of growth. Similarly, we know some of the highest intensities 
which can be tolerated. 
For growth at the base level of existence, there is only required the 
almost immeasurably small food supply of conductivity water, a scanty 
amount of free oxygen, and a temperature of 6° C.—perhaps lower. 
These factors may be increased in. intensity until there is tolerated a 
food supply enormously larger, abundant oxygen, and temperatures up 
to 37 0 C.—perhaps higher. But as the simple minimum conditions are 
passed, the interactions of the component factors of the environment 
increase, and new factors arise which also have their limits. With 
