Tropistic Movements of Plants . 85 
in reducing power may be observed during a sufficiently long time. Or 
more homogentisinic acid may be introduced at first to extend the time of 
observation still more. 
When so much homogentisinic add is added, the slight error caused 
by the simultaneous presence of other reducing substances in the mixture, 
such as sugar, can be still more neglected. Since, after some time, no 
reduction at all can be observed in the specimens, even these substances 
must be destroyed by enzymes. 
IV. 
We must now pass on to a criticism of the results of our experiments. 
Even if between geotropically stimulated and unstimulated roots there 
exist constant and certain differences revealed by the anti-ferment test, 
we must meet the objection that the anti-ferment reaction may not be 
confined to tropistic stimulation, but may accompany a variety of departures 
from the normal condition of plant organs. Therefore it must be shown 
that only tropisms are able to produce the anti-ferment reaction. This can 
be really shown, and the following results demonstrate that neither chloro- 
form-narcosis nor poisoning by antipyrin, acids, alkalies, nor mechanical 
hindering of growth by means of gypsum, nor traumatic stimulus, are by 
themselves able to produce anti-ferment reaction. 
When chloroform or any other poison was used, the proper concentra- 
tion was empirically determined in each case, namely, the strength neces- 
sary to prevent growth and curvature without permanent injury, during 
the period experimentally known to be sufficient for geotropism to occur. 
In order that the roots may be certainly influenced by the poison, they 
must stand in the solution during a sufficient time (one hour at 16 0 C.) in 
the vertical position, before they are geotropically stimulated by placing 
them horizontally. 
Before beginning the chloroform experiments I convinced myself 
that the anti-ferment reaction occurs in the same degree in roots kept in 
damp air as in 
roots entirely 
submerged in water. 
The reducing power 
of 5 cc. of the filtrate tested in equal intervals of time 
was found to be — 
Unstimulated : 
Stimulated by placing them horizontally for thirty minutes : 
in damp air. 
in water. 
in damp air. 
in water. 
3 -o 
3 *° 
3.0 
3-0 cc. — AgNOs 
10 
2-5 
2*5 
2-8 
2 *7 » v 
2-1 
2*1 
2-6 
2'4 1, 
i *7 
i*6 
2.3 
2*1 „ 
The reducing power was, as usual, exactly equalized at the beginning 
of the experiments. Even between roots growing in damp sawdust and 
growing in water no difference was noticed. The water (from the water 
supply) had therefore no influence on the degree of anti-ferment reaction. 
