274 BOTANICAL GAZETTE [APRIL 
capable of oxidizing various organic substances such as guaiacol, 
pyrogallol, and gallic acid. His work showed that there was con- 
siderable active secretion on the surface of growing roots and that 
this secretion had definite powers to effect changes in organic 
substances. CzAPEK (10) repeated some of the investigations 
made by Motiscu and raised some doubt as to the correctness of 
Motiscu’s conclusions. The fact that roots have oxidizing powers, 
as set forth by Motiscu, has been well corroborated, however, 
by the investigations of RActBorsKI (11), who used a number of 
reagents and widely different plants. He did not find a phanero- 
gam, the roots of which did not have the property of extracellular 
oxidation. Great differences, however, existed between the oxi- 
dative powers of different plants. 
Two classes of substances have been found useful in showing 
the oxidizing power of roots in solution culture. The first class 
comprises certain soluble chromogens which yield upon oxidation 
insoluble compounds mainly deposited upon the surface of the 
roots. The second class of chromogens consists of certain sub- 
stances which give soluble coloring matter as the result of the ox 
dizing action of the roots, shown by the change from a colorless to 
a colored compound or by a change from one color to another 
which is distinctly different. Compounds belonging to the first 
class are alpha-naphthylamine, benzidine, vanillin, vanillic acid, 
and esculin. The second class of chromogens is in many respects 
more useful for oxidation studies, because the intensity of the 
color and hence the amount of oxidation can be quantitatively 
expressed. Among these substances are phenolphthalein, aloin, 
and leucorosolic acid. : 
When organic substances like alpha-naphthylamine and benzl- 
dine in solution of ro p.p.m. and 5 p.p.m., respectively, are used, 
the colors due to oxidation are shown on the root. The most 
marked oxidation is shown by a narrow but very distinct band of 
color just back of the root cap. Then comes a practically color- 
less zone and then a broad colored zone, the color becoming less 
intense toward the upper part of the root. When a 0.04 per cent 
solution of aloin is used, a diffusion zone of color is at first formed 
close to the root, but in the course of a few hours the solution, a5 4 
