_ 278 BOTANICAL GAZETTE [APRIL 
the two deposits of color on the roots were so nearly alike that it 
was difficult to tell whether selenium had been deposited or not 
in connection with oxynaphthylamine. In solution of benzidine, 
5 p.p-m., the roots as a whole had a blue-black appearance, and a 
heavy ring appeared just back of the root cap. In the same 
strength of benzidine plus 0.25 per cent sodium selenite, /t000 
acid to phenolphthalein, the black oxidation ring at the root tip 
still appeared, but the roots, as a whole, were pink from the de- 
posited selenium. In 0.04 per cent aloin and o. 15 per cent sodium 
selenite made /500 acid, some oxidation of the aloin solution 
occurred and a good reduction of selenite. In aloin and sodium 
selenite 2/1000 acid, there was strong oxidation and slight reduc- 
tion. 
The experiments show that it is possible to have oxidation and 
reduction by the same roots in the same solution. A slightly acid 
reaction is favorable to reduction, a slightly alkaline reaction 
favorable to oxidation. Between these acid and alkali limits 
both processes are demonstrable as occurring side by side. 
It has long been supposed that oxidation by the plant roots and 
plant extracts is due to the presence of oxidizing enzymes, such as 
the oxidase, peroxidase, and the related catalase. A good review 
of the literature on cellular oxidation with consideration of the 
relationship between the enzymes may be found in works of Bact 
(7) and Kast1e (8). 
According to Bacu, the oxidase is a mixture of peroxidase and a 
peroxide-forming substance. The enzymes taking part in cellular 
oxidation are according to him oxygenase, peroxidase, and cata- 
lase. He explains their relationship as follows: (1) In order to 
have at its disposition a continued source of active oxyget, the 
living cell produces oxygenases or bodies capable of fixing atmos 
pheric oxygen with the intermediary formation of peroxides; (2 
the peroxides thus formed are activated by the peroxidase in the 
way that hydrogen peroxide is activated by ferrous sulphate; the 
system peroxidase-peroxide effects the oxidation of substances Ser" 
ing as aliments to the cell, substances which are oxidized with 
difficulty; (3) in cases which are particularly favorable to the 
formation of peroxide, excess of which might be injurious to the 
