93 
Tropistic Movements of Plants . 
not occur on the klinostat is a question for further investigations. I should 
suppose that probably extremely small curvatures do take place, which 
are easily neutralized by the ortho-autotropism of roots, i. e. the tendency 
to grow in a straight line ; moreover, there must exist interferences between 
the curvatures. 
VII. 
My researches on various other applications of the anti-ferment test to 
geotropical questions, e. g. to the problem of the geotropism of secondary 
roots, will be reserved for another paper. Here I shall only enter upon the 
use of the method in a single problem — the question of the geotropic 
sensitiveness of the root-tip, which has received so much attention since 
the famous experiments by Charles and Francis Darwin. This problem has 
gained a new interest from the views established by Nemec (21), Haber- 
landt ( 22 ), Francis Darwin ( 23 ), the so-called ‘ statolith hypothesis/ 
As is known, Nemec supposes that the displacement of starch-grains 
in the young cells of the root-cap supplies the mechanism of perception, 
and that only the root-tip (more exactly the part containing the young 
root-cap cells) can perceive the geotropical stimulus. To this view, which 
has been supported recently by experiments published by Francis Darwin, 
which harmonize with other physiological experiences, I have especially 
objected as follows : that in my experiments with glass tubes much more 
than the root-cap must be bent ; at least i*5 mm. of the root-tip must be 
bent laterally before the perception-zone is entirely separated from the 
zone of growth and curvature. I further succeeded in demonstrating, in 
one of my later papers, that the accumulation of homogentisinic acid in 
decapitated roots could only be hindered by cutting off i*5 mm. of the 
root-tip. 
There remains to complete these experiments by applying the better 
and stricter anti-ferment test. 
One hundred roots of Lupinus albus , from which 0*5 mm. of the tip 
had been removed, were placed in a vertical position in sawdust ; another 
lot of one hundred roots treated in the same manner were placed horizon- 
tally for thirty minutes. Then all the tips were ground and prepared for 
the test. The reducing power decreased in the following ratio 
Unstimulated roots 2-0 i*6 1*2 o-7cc. ~AgN 0 3 
Stimulated roots . 2-0 1-7 14 1-2 „ „ 
The same experiment, cutting off i*o mm. of root-tip : — 
Unstimulated roots 2*0 1 *6 1.2 0-7 o-o cc. ^AgNO s 
Stimulated roots . . 2*0 i-8 1 -6 1.3 0*7 „ „ 
