158 
THE PLANT WORLD. 
time after the stimulus of gravity begins to act, an accumulation 
of homogentisinic acid. The influence of gravity, therefore, 
retards the effects of the oxydase. 
By further experiments it was determined that a special inhib¬ 
itory substance is formed as a result of the geotropic stimulus. 
The same phenomenon takes place in all tropistic movements so 
far investigated. This substance has the properties of an enzyme 
and “ may be characterized as an anti-oxydase, on account of its 
effect being contrary to that of the oxydase of the root tips. The 
anti-enzyme produced in geotropically stimulated hypocotyles of 
Lupinus affects the oxidizing enzyme in the Lupinus root tip, but 
not the enzyme of root tips of Zea Mays or Cucurbita. Further¬ 
more the anti-enzyme produced in phototropic or other tropistic 
stimulation does not differ at all from the anti-enzyme produced 
in the same plant by gravity. The anti-enzyme does not exist 
in unstimulated roots, and after curvature has taken place, fol¬ 
lowing stimulation, there is found no difference in the amount of 
the homogentisinic acid in the stimulated and unstimulated roots. 
It has been demonstrated that the root tips of seedlings rotated 
horizontally on the klinostat show the presence of the anti¬ 
enzyme, indicating that the stimulus has been received. Thus 
arises a question full of interest for the plant physiologist as to 
why the root does not bend. This question is as yet unanswered. 
Wounds and extremes of light and heat cannot cause the anti¬ 
enzyme, but all tropistic stimuli cause it in root tips, cotyledons, 
stems and other parts. The accumulation of the acid is inhibited 
by cutting off 1.5 mm. of the root tip and the “ anti-ferment reac¬ 
tion ” takes place in excised portions of the tip of only 5 mm. in 
length. Also, in roots of Lupinus albus, which do not curve in 
response to the stimulus of light, the anti-ferment results. 
The author does not consider the statolith hypothesis as wholly 
refuted by his work, though some stimulation effects are present 
when all the cells containing statolith starch are cut away. 
C. S. G. 
