The Anti-ferment Reaction in Tropistic 
Movements of Plants 1 
BY 
FREDERIC CZAPEK, Ph.D., M.D. 
Professor of Botany in Prague 
I. 
0 determine whether or no an external stimulus has been perceived by 
JL a plant we have generally only one method : namely, to observe 
whether or not a movement follows the stimulus. The positive observation 
of a distinct movement is a proof that the stimulus has been perceived. 
When no distinct movement is to be found, it is possible, either that the 
stimulus has been perceived, but that a movement for some reason could 
not be carried out, or that the external stimulus was not perceived. 
Therefore in such experiments negative results cannot be utilized. 
Positive results, moreover, depend exclusively upon observations made on 
the motor zone. Where perception of stimulus and reaction take place in 
separate zones of the organ, as in the geotropic perception of the root-tip, 
discovered by the Darwins, father and son, and in the geotropic curvature 
in the motor zone of the root, no processes can be detected in the sensory 
zone by the general method of investigation above mentioned. 
My wish to gain some knowledge of what goes on in the sensitive root- 
tip was realized in 1897, after much fruitless endeavour (1). 
A number of root-tips of Vicia Faba major , half of which had been 
geotropically stimulated, while the remainder were unstimulated, were 
treated in the following manner. Thick longitudinal sections were prepared 
and boiled in an ammoniacal solution of silver nitrate : they all gave 
a strong reduction. But when the specimens, carefully squeezed on the 
slide with the cover-glass, were held towards the light, it was clear that the 
stimulated tips were always darker than the unstimulated ones. This 
difference was already distinct long before the first beginning of the 
geotropic curvature. Another result was found in the fact that unstimulated 
root-tips placed in a water-emulsion of alcoholic guaiacum solution were 
coloured blue before the stimulated root-tips ; in the same manner the 
colour tests with alkalin solution of a-naphthol + p-phenylen diamin, or 
with reduced indigo, were retarded to a remarkable degree. I succeeded 
therefore at this time in demonstrating the action of an oxydase in the 
three tests mentioned. But I could not decide whether the decrease in 
oxydasic effects (after a geotropic stimulation) is caused by a quantitative 
1 Read before the Botanical Section of the British Association, Cambridge, August, 1904. 
[Annals of Botany, Vol. XIX. No. LXXIXI. January, 1905.] 
