97 
Tropistic Movements of Plants. 
Roots of Lupinus or of other seedlings equally illuminated on all sides 
never gave any anti-ferment reaction. This is proved by the following 
experiment with roots of Lupinus. Two lots of ioo roots were placed 
vertically in damp air in glass troughs ; their cotyledons were wrapped in 
wet cotton wool. One of the troughs was covered with an opaque box, the 
other was illuminated from both sides by equidistant incandescent lights 
during two hours. The reducing power in this experiment decreased in 
the following rate : — 
Darkened . 2*0 i*6 11 0*7 cc. ~ AgNO s 
Illuminated 2-0 1*7 1-2 o-8 „ „ 
There was, therefore, no distinct difference ; in other words, only lateral 
illumination gives an effect. In the above experiments the heating effect 
of the lamps has not been considered. To test this possibility, large glass 
dishes 20 cm. wide were placed before the troughs containing the roots, 
and through the dishes a stream of cold water was allowed to flow. 
During the two hours that the experiment lasted the temperature was 
taken at three places, and it was clearly ascertained that the temperature 
on the illuminated side was not higher than on the dark side. The roots 
were then prepared and tested in the usual way. The decrease in reducing 
power was : — • 
Control . 2-o 16 i*i 0-7 cc. — AgN 0 3 
Illuminated 2-0 i-8 1-5 12 ,, ,, 
In spite of excluding any local effects of higher temperature the anti- 
ferment reaction was found to be distinct. 
Another experiment, analogous to this, but made with roots growing 
in damp air, gave the following results : — 
Control . 2-0 i-6 1*2 o-8 cc. ~ AgN 0 3 
Illuminated 2*0 i-8 1-5 1-2 „ ,, 
I consider it, therefore, an undoubted fact that lateral illumination 
alone (under the conditions generally necessary for heliotropic curvature) 
is able to produce anti-ferment reaction in all seedling roots. We have 
certainly a right to consider this a rudimentary tropistic reaction, and these 
experiments are the only ones up to the present time that can demonstrate 
the general occurrence of heliotropism in roots. We may hope that the 
anti-ferment reaction will prove to be an available method for demonstrating 
sensibility to tropistic stimuli where no curvature or only uncertain 
reactions are observable. I have here in mind chemotropism, osmotropism, 
thermotropism in roots and in other plant organs. Investigations of these 
questions will be carried out in my laboratory. 
H 
