Pfeffer. — Geo tropic Sensitiveness of the Root-tip . 319 
But with this object it is possible to demonstrate with 
certainty that only the capacity to perceive the stimulus has 
been lost by wounding, but not the capacity to conduct 
a stimulus already perceived. For if we expose the tip of 
a leaf to light for only a short time, and cut it off before 
curvature is noticed, the heliotropic reaction takes place in 
the wounded leaf precisely as in an uninjured one, although 
through wounding the sensitiveness of the leaf has been 
suspended. 
In an entirely analogous way, a reaction manifested in 
geotropic curvature takes place in roots when they are de- 
capitated after geotropic induction. That, however, only 
proves that an actual geotropic induction is not necessarily 
connected with the continual existence of sensitiveness. The 
attempts made to prove from this fact the sensitiveness of the 
root-tip are in so far based on incorrect inferences. 
As regards heliotropism the state of things is easily 
demonstrated, since the rays of light that act as a stimulus 
can easily be directed to a single point. On the other hand, 
it can hardly be thought of as practicable to expose the root- 
tip alone to the stimulus of gravitation, or in place of this 
to centrifugal force. We attained the end in another way, 
however, namely by compelling the tip of a root, whilst 
growing quite normally, to permanently take up a position 
at right angles to the rest of the root. 
For this purpose we allowed roots of Faba , Lupinus , &c., 
to grow into short tubes of thin glass that were bent at a 
right angle. The advancing root easily follows the bend 
of the tube and pushes on as far as the other end which has 
been closed by heat. Corresponding to the shape of the 
glass, there is now a terminal portion of the root, 1, 5 or 
2 mm. long, at right angles to the rest of the root, of which 
again 1, 5 or 2 mm. occupies the other arm of the tube. 
This condition of things is continuously maintained, since, 
with its growing region in the tube, the older parts of the root, 
like plastic wax, are pushed out of the glass cap. 
To prevent geotropic stimulus, the roots were made to 
