The Hydrion Differentiation Theory of Geotropism 79 
^requiring days for its accomplishment,” these particles may slowly 
produce potential differences which would continue the action cur¬ 
rent 1 initiated by the ‘'creaming” of the larger particles. Now, if 
we suppose a potential difference to be developed in each cell on 
displacement of the organ, we have the possibility of an action 
current for several days. Further, only merisiems are supposed to 
be geotropically perceptive , at any rate in the higher plants. Cell 
division in meristems is frequent, and some cells are always in the 
process of division. During cell division there is naturally a more 
or less complete redistribution of the dispersed particles, and each 
daughter cell may be considered as showing “ creaming ” for at least 
several days after its formation. It will be remembered that, when 
the main apical meristem becomes inactive in any way, its functions 
are taken over by a lateral branch. Since the “normal polarity 
current ” is dependent upon the meristematic activity and controls 
the angle of the lateral organs, the disappearance of that activity 
involves the disappearance of the control of the lateral organs, until 
one of these assumes the vertical position, and takes over control 
by producing a “normal polarity current” instead of an “action 
current.” 
Professor Blackman then proceeds to quote two experiments 
by Bose. These can be dealt with briefly. In the first there is no 
evidence that the electrode position in the endodermis was distin¬ 
guished from a close approximation to the adjacent meristematic 
region of the cambium, which might have been the gravity-percep¬ 
tive region in that case. The second is surely a special case, since 
Bose himself has recently 2 stated that “the electrical response is 
found to increase as the sine of the angle of inclination,” and he is 
supported on this point by the observations of Fitting and the 
writer 3 . Since the phenomenon is exceptional, even in Bose’s experi¬ 
ments, it follows that a special enquiry is necessary and a special 
explanation probable. 
ProfessorBlackman supposes that my theory “rejects the move¬ 
ment of comparatively large cell particles (such as starch grains) as 
the first step ” and quotes the experiments by Bose in support of 
the statolith hypothesis. The presence of statoliths and of gravity 
1 Possibly to a lesser degree, but the smaller movement might be compen¬ 
sated by the greater number of smaller particles and the resulting possible 
increase in total potential difference. 
2 Nature, 22nd July, 105 , p. 650. 
3 See Proc. Roy. Soc. B. 90 , pp. 349-360. 1918. 
