82 Frederic Czapek . — The Anti- ferment Reaction in 
power after geotropic stimulation can easily be shown in all root-tips, 
hypocotyls, epicotyls, and, speaking generally, in all organs of plants hitherto 
investigated by me (7). The increase in homogentisinic acid always 
appears much earlier than the first traces of geotropic curvature, and the 
maximum is observed after about thirty minutes in roots kept at i8° to 
20° C. The same phenomenon is also generally to be found in phototropic and 
hydrotropic movements (8) ; it has not in fact been absent in any tropistic 
movement investigated up to the present time. When the roots have 
finished their geotropic curvature, the difference in the amount of homo- 
gentisinic acid in comparison with vertical roots is nearly imperceptible. 
The course of the process may be illustrated by the following figures, giving 
the result of the titration of io cc. of filtrate (entire filtrate 25 cc.) obtained 
from 100 ground-up roots of Lupinus albus which had been previously 
stimulated : 
Duration of geotropic -- AgN0 3 used for 10 cc. of filtrate 
stimulation. 
m 100 in 100 
Minutes. 
stimulated roots. 
control roots. 
Difference. 
5 
2-1 CC. 
2-0 
CC. 
0-1 cc. 
10 
2-0 „ 
55 
0-0 „ 
i5 
2*0 „ 
55 
0-1 „ 
20 
2-2 „ 
55 
01 „ 
25 
2-2 „ 
55 
o-3 5, 
30 
2*4 55 
2*1 
55 
°*3 » 
45 
2*3 5, 
2-0 
55 
o*3 5, 
60 
2*15 55 
Curvature distinct . 
!*9 
55 
0-25 „ 
90 
2*15 55 
2-0 
55 
0*15 5, 
120 
2-25 „ 
Curvature finished . 
2-15 
55 
0.1 „ 
180 
i-9° 5, 
55 
0-0 „ 
The observed differences are certainly above the limits of error of the 
method. But they are, however, so small, that they can only be regarded 
as just certain differences, since the quantities are very small and the error 
of the method rises to 10 per cent, of the values obtained. It became, 
therefore, a matter of importance to obtain control of a method giving 
a much closer insight into the metabolism of stimulation than could be got 
from the direct estimation of homogentisinic acid. 
III. 
The inhibition of oxidase action which I found accompanying an 
accumulation of homogentisinic acid must be assumed (in accordance with 
my present experience) to be in causal connexion with the increased values 
obtained by silver-titration. 
It is easily demonstrated that the ground-up root-tips kept for some 
