Electricity—-Radium-, N-, and X-rays 
The electric light can be and is often used instead of 
sunlight, and the results are sometimes of great value 
financially. Lilac can be made to flower ten days 
sooner by using arc-lamps. 
Semon managed to get certain acacia seedlings to do 
with a twelve-hour instead of a twenty-four hour day by 
electric light cultivation. A regular rhythm could be 
induced corresponding to six hours instead of twelve 
hours of light.’ 
We have already shown how interesting and practi- 
cally useful are the points connected with electric light 
and electric stimulus on vegetable life, and it is neces- 
sary to say something about the effects of radium- 
and Roéntgen-rays. 
This need not take up too much space, for, so far as 
is now known, such rays seem to be always cither harmful 
or without any influence whatever. Bacteria are killed, 
growth is prevented, and the germination of seeds is 
hindered by them. The nucleus of the cell is also said 
to be affected injuriously.® 
On the other hand it is said that af first there may be 
a slight increase in growth or favourable effect under 
either Roéntgen- or radium-rays, which is soon followed by 
a greatly retarded or complete cessation of growth. This 
is, however, exactly what is found in the case of most 
poisons (see Chap. XXIX.). Bacterial spores are killed 
by radium in seventy-two hours and vaccine in twenty- 
two hours.” 
But after such micro-organisms have been destroyed, 
that is, after 24 to 120 hours’ exposure, it is found that 
they themselves, though dead, become radiant. A feeble 
radio-activity is also said to be exhibited by freshly 
gathered vegetables, but only lasts for at most four days.4 
Recently Dr. Russell discovered that photographic 
plates can be affected in the dark by a great variety of 
216 
