394 
Bayliss. — On the Galvanotropism of Roots . 
4 c. Summary of Results with Polarizable Electrodes. 
From these results it will be seen that a strong electric current applied 
to the root for a short time will produce just the same kind of curvature as 
a weak constant current for a long period, and that the direction of the 
curvature evidently depends on the position of the electrodes, not on 
whether the current is strong or weak. 
If both the electrodes are on the sensitive zone of the root, and the 
same distance from the apex on opposite sides, the curve is always to 
the positive electrode. 
If one electrode is on the sensitive zone, and the other some distance 
away, either on the same side or opposite side, the curvature is always 
towards the apical electrode, whether positive or negative. A few experi- 
ments performed without the use of a clinostat showed that electrical 
stimulation could produce curvatures even in opposition to the stimulus 
of gravity. 
Some lateral roots were tested and gave similar results to primary 
ones. 
4 d. The Angle of Curvature. 
The angles of curvature were usually sharp, and varied in extent from 
a few degrees to i8o° or more, according to the duration and amount 
of stimulation (cp. Fig. i). After about twenty-four hours or less the 
effect of the stimulus passed off ; the autotropic tendency of the root would 
then assert itself, and the last centimetre or so would take an ‘ S ’ form. 
Sometimes when the stimulation had been feeble and the curve only slight 
the root straightened itself completely. 
4 e . The Sensitive Zone. 
To find the length of the sensitive zone of the root the position of one 
or both electrodes was varied from time to time, and beyond the fourth or 
fifth millimetre from the apex no response to stimulation took place. The 
most sensitive part was at from i mm. to 2 mm., but a slight curve could be 
obtained even when one or both electrodes were placed 4 or 5 mm. from 
the root-tip. 
4 /. Decapitated Roots. 
With decapitated radicles there was usually no response, either when 
decapitation took place before stimulation or when stimulation preceded 
decapitation, as the following results show : — 
ii radicles with 1-5 or 2 mm. of their tips cut off were stimulated, and 
of these 8 remained straight, 2 curved slightly, and 1 curved 30°. 
