89 
Tropistic Movements of Plants . 
stimulation is necessary for anti-ferment formation. This is the shortest 
period in which geotropic stimulation has hitherto been shown to occur. 
Formerly I showed ( 11 ) that geotropic after-effect on the klinostat can 
only be detected in roots of Lupinus or other sensitive objects after more 
than fifteen minutes of geotropic stimulation. This * presentation-time ’ 
for geotropic curvature is therefore much longer than the ‘ presentation- 
time ’ for the anti-ferment reaction. If the roots, having been horizontal 
during six minutes, are allowed to grow vertically, it is possible to find out 
how long the anti-ferment reaction continues. Under these circumstances 
the reaction is found slightly diminished after one and a half hours, very 
much diminished after two and a half hours, and it finally disappears after 
four hours at I 7 °C. Thus those parts of the geotropic process which are 
not externally perceptible come to nothing, precisely as is the case with the 
visible part of the phenomena. For a root left horizontal for fifteen minutes 
and then placed vertically shows no visible curvature. For stimulation of 
six minutes’ duration the klinostat fails us as a method of observation, and 
we have only the anti-ferment reaction to rely on. 
When the roots are placed horizontally for longer than six minutes 
the anti-ferment reaction is observed in about the same intensity as after an 
induction of six minutes, during at least three hours after the close of the 
stimulation. The maximum of the reaction is reached very quickly : thus 
between stimulation-periods of six and fifty minutes no quantitative 
difference can be observed in anti-ferment reaction ; it may be added that at 
a temperature of 15-20° curvature is usually beginning after fifty minutes. 
The anti-ferment reaction therefore differs from after-effect test, which occurs 
much more strongly after thirty to forty-five minutes than after fifteen 
minutes of geotropic induction. The duration of the anti-ferment reaction 
after the cessation of stimulation was also determined. When the stimulus 
lasted ten minutes the anti-ferment test could no longer be observed 
eight hours after stimulation. After inductions of twenty minutes the anti- 
ferment reaction seems to come to its end in eight hours. But when the 
roots were stimulated for thirty minutes the anti-ferment reaction did not 
disappear earlier than twenty hours after the close of the induction. With 
forty and fifty minutes’ stimulation twenty-four and thirty hours are needed 
for the anti-ferment reaction to run its course. The effect is therefore more 
persistent the longer the geotropic reaction continues. As is known, the 
after-effect on the klinostat increases in a similar manner. The curvature 
due to after-effect disappears under the straightening influence of auto- 
tropism more easily in proportion as the stimulation is of short duration. 
In the same way the curvature appears later after a short stimulus than 
after a longer one. Thus the curvature of roots stimulated for twenty 
minutes is observed after twelve to twenty-four hours, of roots stimulated for 
thirty minutes after eight hours, of roots stimulated for forty minutes after 
