Electricity—Radium-, N-, and X-rays 
to the stem and leaves, where there may be discharges 
into the atmosphere. 
There is some support for this theory, as one can 
at once prove by directly testing living plants. When 
the ascent of sap is slow and feeble the current may 
be imperceptible, but a distinct though feeble current is 
usually to be found when the sap is flowing vigorously. 
Several authors have found that currents which are 
made to pass in the reverse way, that is, from the top 
of the stem towards its root, produce injury, whilst those 
in the direction of the sap are distinctly favourable. 
That feeble currents of electricity stimulate germina- 
tion and the growth and vigour of a plant seems to 
be admitted by all authorities. Indeed it has been 
shown that a weak electric current stimulates the 
streaming movements of protoplasm, whilst a strong 
current has the opposite effect and retards it. 
So also with various specially sensitive plants. Dr 
Bose has obtained reactions which strangely resemble 
what happens when animal protoplasm or even muscles 
are similarly stimulated. The stamens of certain 
Centaureas contract, just as they do when touched by 
an insect’s foot or a needle. A piece of convolvulus 
stem contracted about three per cent. of its length 
under small shocks at five seconds interval. For other 
examples one must refer to his book upon the subject. 
There is also plenty of evidence to show that electric 
currents help in assimilation. The Canadian water- 
weed (Elodea) has often been used to test this point. 
By passing an electric current through the water in 
which it is growing, the number of air-bubbles given 
off per minute is distinctly increased, and, if one is 
careful to keep the current weak enough, the plant 
is not injured. But it is very easy to tire it out 
by overstimulation and so kill it by electrocution.’ 
212 
