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. 8 



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 Rontgen-rays. 



This need not take up too much space, for, so far as 

 is now known, such rays seem to be always either 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. 9 



On the other hand it is said that at first there may be 

 a slight increase in growth or favourable effect under 

 either Rontgen- 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. 10 



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. 11 



Recently Dr. Russell discovered that photographic 

 plates can be affected in the dark by a great variety of 



216 



