Electricity—Radium-, N-, and X-rays 
These experiments are of course distinctly encourag- 
ing, but whether the cost of producing even a 50 per 
cent. increase of the crop will prove economical or not, 
is a question which can only be solved by many trials. 
There is also the danger of electrocution. In America, 
strong electric currents are used to destroy the railway 
weeds (see p, 258). Continuous electric currents for 
street cars have also been found to destroy trees, 
especially in wet weather. Alternating currents seem 
to stimulate the growth of trees, but this is sometimes 
injurious.® 
In America, where long distance transmission lines of 
high voltage are common enough, secondary induction 
currents must often be set up in any trees which happen 
to be growing close to the wires. That this is really 
the case seems certain from Major Squiers’ experiment. 
He found that on attaching a telephone to the trunk of 
any tree within a hundred yards of such a line, a distinct 
note could be heard due to the induced current. These 
trees had been “singing” the same note without any 
rest for years ever since the line had been built.* 
_ When an electric discharge is passed through ordinary 
air, both nitrogen and hydrogen are affected, nitrous 
and nitric acid are formed, and also peroxide of hydrogen. 
It is probably these substances which are responsible 
for the destruction of bacteria,®> but ozone is also pro- 
duced, which is again a bactericide. Ozone affects yeast 
injuriously, and also those ferments or enzymes which 
play an important part in every physiological process in 
plant life.° 
Pollacci has suggested that the process of assimilation 
depends upon electrical currents in the leaves, and it is 
as we have seen, a fact that peroxide of hydrogen is really 
formed by electric discharges in the atmosphere.’ 
* See ‘‘ Romance of Plant Life,” p. 198. 
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