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.^ 



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