392 
Bayliss. — On the Galvanotropism of Roots . 
so placed that the roots were horizontal and parallel to the axis of rotation, 
and at right angles with the incident light. 
When working with very weak currents a more complicated apparatus 
was used. A glass cylinder 30 cm. x 8 cm. was fitted at either end with 
a cork, through which a glass rod was passed. This cylinder was so attached 
to the clinostat that the glass rod constituted a horizontal axis of rotation, 
and its end remote from the clinostat rested upon friction wheels (Fig. 2). 
Surrounding the cylinder at each end was a ring of wire with radiating 
projections. Beneath each ring was a small vessel of mercury, and as the 
cylinder revolved the projections dipped into the mercury. Inside the 
cylinder the glass rod passed through a large cake of paraffin wax, which 
served as support for two small platinum electrodes, and wires from these 
passed out of the cylinder at opposite ends, and were joined up with those 
forming the rings. A cork disc arranged parallel with the other corks 
served to support the seedling, so that, when the electrodes touched the 
radicle, and the ends of the conducting wires from the battery were dipping 
in the vessels of mercury, a complete circuit was formed. 
The same precautions as before were taken to ensure moist and 
oxygenated air. 
For some time there was a great difficulty in getting a current which 
after passing for some hours did not kill the roots. For the supply of 
electricity an accumulator of voltage 4-2 was used, and in the circuit at first 
was placed a resistance box of 14,000 ohms. This current proved too 
strong, so water resistances, in the form of 1, then 2, then 3 metre-length 
tubes filled with very slightly acidulated water, were added. The current 
now seemed about the right strength, but was so feeble that it could not be 
measured even by a milli-ampere metre. 
After ten days or so the water resistances did not act well, owing 
to polarization, and had to be discarded. Ultimately instead of the 
accumulator a dry cell, voltage 1-35, was used, and this with two resistance 
coils of 100,000 ohms, and 50,000 ohms, respectively, gave a workable 
E 
current, and one easily measured from the formula C — — . The 
R 
150,000 ohms, resistance was so great as to render the other resistances 
negligible. 
With these two kinds of apparatus electric currents were passed 
through several hundreds of seedlings — a tedious process, since from the 
nature of the apparatus only one could be treated at a time. 
4 a. Results with Weak Currents. 
Weak constant currents varying in duration from five hours to two 
days, when stronger than — — — ampere, gradually killed roots, but from 
150,000 
