40 T. L. Lyon anp J. K. Witson 
unboiled was brown, and the check was a light yellow. On the whole 
the tests for oxidizing substances cannot be said to have offered very 
strong evidence of their presence except in the case of peroxidases. 
Possible coexistence of oxidizing and reducing substances 
Altho the number of tests for oxidizing enzymes were rather few, reac- 
tions indicating their presence were confined mainly to the solutions from 
flasks which gave no marked response to tests for reducing substances 
It seems likely that both classes of substances are coexistent in solutions 
in which plants are growing, and that at one time the oxidizing substance; 
may be dominant and at another the reducing substances. Difference; 
in the intensities of the reactions at various times may thus be accountec 
for. Apparently with the maize plant the predominating reaction wai 
for reducing substances thruout most of the stages of growth. 
It would appear from these experiments that some form of reducing 
substance is always present in the solutions in which plants are growing 
Whether oxidizing substances are always present, it is more difficult t 
say. They were found in some of the solutions taken from flasks in whicl 
the plants had reached only an early stage of growth, and unless they ar 
destroyed later on they must be present thruout the entire life of the plant 
In the natural soil solution, enzymes might be destroyed and thus remover 
from active operation except when freshly liberated. 
Nature of oxidizing and reducing substances 
Boiling the solutions in which plants had grown completely terminate: 
the activities of the oxidases, as was to be expected. It did not alway! 
have that effect on the reducing substances, especially the nitrate reducers 
There would thus seem to be considerable doubt as to whether the reducin 
substances were enzymic in character, but they at least had the power ¢ 
bringing about reduction of nitrates in the absence of bacteria. 
SUMMARY 
Plants were grown with their roots in large flasks (8 or 12 liters capacity 
containing a nutrient solution, the entire contents of the flasks bein 
sterile. At various stages in the growth of the plants they were remove 
from the flasks and analyzed for nitrogen, and the nutrient solution we’ 
