396 Bayliss. — On the Galvanotropism of Roots. 
but at the negative electrode only a weak alkaline reaction was evident, 
this being probably due to partial neutralization by the C 0 2 of respiration. 
These reactions suggested that possibly touching the sensitive zone of the 
root with acid or alkali might produce similar curvatures to those produced 
by an electric current, so pieces of blotting-paper, i sq. mm. in extent, 
soaked in either a solution of sodium carbonate or sulphuric acid, were 
placed on roots about 1-5 mm. from the apex, with the following results: — • 
Of 11 roots on which decinormal solution of the alkali was placed 
8 curved towards it. 
Of 42 roots treated with decinormal or weaker H 2 S 0 4 , 31 curved 
to the acid, 6 away, and 5 did not curve. 
Of 11 roots on each of which a tiny slice of electrolysed acid tissue 
had been placed 8 curved to the acid. 
Of 11 roots on each of which a slice of electrolysed alkaline tissue 
(or the sap only) had been placed 8 curved to the alkali. 
A few experiments were tried in which decinormal acid and decinormal 
alkali were placed opposite one another, when the curve was to the acid 
side (thus producing a curve analogous to the one obtained when the 
positive and negative electrodes were placed opposite one another). 
These acid and alkaline curvatures could be obtained without injury 
to the root, although when the acid or alkali was strong injury did take 
place. 
7. Latent Period of Response. 
The response to the electrical stimulus is slow, and is not apparent to 
the naked eye until after at least three or four hours at a temperature 
of 1 9 0 to 22° C., while at a lower temperature (15 0 to 18°) often twelve hours 
or more elapse before there is any sign of a curve. With a horizontal 
microscope, however, a curvature can be detected within an hour of 
stimulation. 
8. The Abnormal Thickening of many Roots. 
Accompanying the curvature of the roots there was very frequently 
a thickening just above the electrode which was placed between the apex 
and the fourth and fifth millimetre space (Fig. 3). Microscopic sections of 
this showed merely a slight increase in the size of the cortical cells. This 
thickening appeared even when growth had been stopped for a few days 
by imbedding in plaster of paris. 
This could hardly be a correlative action due to arrest of growth 
at the apex causing an increased tendency to lateral swelling behind, 
for when unstimulated root-tips were fixed in glass caps or glass collars no 
such result was produced. Hence this phenomenon must be due to the 
stimulatory action of the electric current, or more probably of the products 
