Bayliss. — On the Galvanotropism of Roots . 395 
6 radicles were stimulated, and their tips (1-5 mm.) then cut off, and of 
these 5 did not curve. 
In these experiments electrodes were applied from 1*5 to 2 mm. from 
the apex, and then just the tip or 1-5 mm. of the root was removed. 
4 g . Duration of Stimulus. 
To find the duration of stimulus, roots were stimulated with strong 
currents, as in 4 b ( a ), fixed in plaster of paris, and rotated on a clinostat. 
On opening the casts after one or two days and again rotating, there was 
a curvature in an hour or so, but after three or four days in the plaster fre- 
quently no curvature took place. For example, 7 radicles were stimulated 
and put in plaster of paris, and released at the end of one or two days and 
all curved : whereas of 12 radicles similarly treated but released after 
three or four days, 7 remained straight and only 5 curved. 
■ 
5. Experiments with Non-Polarizable Electrodes directly 
APPLIED TO THE ROOT. 
Some experiments were made, using non-polarizable electrodes with 
the platinum electrodes in the circuit, and at the same time control experi- 
ments, using platinum electrodes with the non-polarizable ones in the 
circuit, so that the total resistance was the same in both cases. 
The non-polarizable electrodes were made by fitting a small brush 
of camel’s hair into a tiny tube 1-5 cm. long, down the centre of which 
extended a copper wire from the accumulator : the brush was kept moist 
by diluted slightly acid cell-sap extracted from pressed roots, slowly flow- 
ing down from the glass tube. The current from the lighting main 
(220 volts) was used, and a large resistance of 2,200 ohms, in the form 
of three resistance lamps arranged in series was added. 
The current was passed for fifty seconds ; 54 roots were separately 
tested, and out of these 43 remained straight and 11 curved, but only 
slightly in most cases. 
In the control experiment 40 roots were tested, and of these 9 remained 
straight and 31 curved, and these very frequently showed scars and other 
signs of injury. 
The non-polarizable electrodes seldom caused any injury. When 
the 220 volt current was passed for longer than fifty seconds, even with the 
non-polarizable electrodes, a curvature took place. 
6. Action of Local Acid and Alkali. 
To ascertain whether there was any appreciable production of acid 
or alkali the cell-sap near the electrodes was tested with litmus-paper : 
there w r as a well-marked acid reaction at the positive electrode contact, 
