Bayliss. — On the Galvanotropism of Roots . 401 
possibly because of the nearness of the electrodes to one another. (Section 
4 b, d and e.) 
6 . When a current is passed through gelatine in which a number 
of roots are growing, both kinds of curvatures take place. (Section 3.) 
7. When non-polarizable electrodes are used, with a strength of current 
sufficient to produce a curvature if applied by polarizable electrodes, no 
curvature takes place. (Section 5.) With these electrodes any acid or 
alkali would be chiefly formed in the glass tubes, and diffusion would 
hardly take place with sufficient rapidity for the acid or alkali to be long 
enough in contact with the root to cause a curvature. 
13. Theory and Critical. 
During the passage of an electric current through a root there are 
two influences to be taken into account : — 
(1) The accumulations of ions near the electrodes, (2) the ions en route 
between the electrodes, either or both of which may be concerned in the 
tropic response. 
Taking into consideration the action of either the acid or alkaline ions, 
it will readily be seen that a stimulus given by the accumulation, say, 
of acid ions will act in a direction quite contrary to that of travelling acid 
ions ; and thus in the case of a current across a single root between directly 
applied electrodes there would be four possible stimulatory actions coming 
into play, namely those due to the accumulated acid ions and the travelling 
alkaline ones acting in one direction, and the accumulated alkaline ions 
and the travelling acid ions acting in the opposite direction ; and the 
response would depend on whether one set of stimuli predominated over 
the other. 
Since with transverse currents directly applied a curvature to the 
positive electrode is always carried out in preference to one to the — elec- 
trode, it is evident that the acid ions have a greater stimulatory effect than 
alkaline ones ; and this is what might be expected, since it is. a well-known 
fact that acid ions travel, and hence accumulate, more quickly than alkaline 
ones, and also are more chemically active. 
Where the current traverses the root longitudinally, the curvature 
no doubt is due to the stimulating action of whichever ions have accumu- 
lated in the sensitive zone, since this region, being the actively growing one, 
is the only part of the root capable of curving. 
Now, comparing the effects of a transverse current acting directly 
on a root, and one passing through gelatine, in which a number of roots are 
growing, a striking difference is apparent. It was remarked in this latter 
instance, that the curvatures in that portion of the gelatine which was inter- 
mediate between the zones extending about 2-5 cms. from either electrode 
were chiefly to the — electrode whether the medium was acid or alkaline. 
