95 
Tropistic Movements of Plants . 
Finally, I cannot exclude the possibility that the anti-ferment reaction 
in decapitated roots is stronger in the part of the root-tip remaining after 
amputation than is normally the case in this upper part of the root-tip. 
Here also the decision is a difficult one. 
On the whole the application of the anti-ferment reaction to the 
question of the localization of the sensory zone demonstrates that all 
stimulation effects are not absent when all cells containing statolith starch 
are as carefully as possible removed. Therefore it may still be doubted 
whether geotropic perception is caused only by means of such cells. But 
the principle of the statolith hypothesis is not yet refuted by the anti- 
ferment experiments, and according to the present state of my experience 
and deliberations I cannot consider the appearance of anti-ferment reaction 
in decapitated roots as refuting directly the hypothesis of Nemec. I say so 
because it is, generally speaking — and not merely in this case — dangerous 
to draw conclusions as to normal processes from the result of operations. 
The statolith hypothesis, however, must explain many other difficulties 
before it can rank as a permanent acquisition to our knowledge. At any 
rate, we gain from it a valuable impulse to new experimental studies. 
What position may now be ascribed to the anti-ferment reaction in the 
chain of processes constituting geotropic action in roots ? As has been 
shown, the anti-ferment reaction takes place long before the curvature, and 
occurs in the root-tip before any alterations can be discovered in the motor 
zone. Further, the anti-ferment reaction is not influenced by the shock of 
decapitation in the same degree as those phenomena of irritability which 
are seriously interfered with when heliotropic and geotropic curvatures are 
for a time checked by injuries to grass seedlings and roots. 
Let us imagine these processes schematically expressed as following each 
other in a chain of consecutive changes 1 . We might, for example, have : 
1. Statolith effect. 
2. Anti-ferment reaction. 
3. The processes which are hindered by shock. 
4. Stimulus transmitted to the motor zone. 
5. Curvature. 
According to this scheme no curvature can exist without anti-fer- 
ment reaction (or some unknown process in causal connexion with the 
anti-ferment reaction). But statolith action can take place without anti- 
ferment reaction, which is shown by roots placed inversely undergoing 
movement of the statoliths, but showing no anti-ferment reaction. It is 
at present unexplained why the displacement of statoliths produces no 
geotropic stimulation in roots inversely placed, in contrast with roots in any 
other positions. In contemplating these remarkable phenomena we are 
reminded of the macula lutea of the retina. 
1 These actions might in reality go on in part simultaneously, and not one after the other. 
