ELECTRICITY AND PLANT-GROWING. 63 



and they are forced into earlier maturity. We are, therefore, able 

 to answer the two questions which we asked ourselves at the 

 outset: 1. There is other influence than mere illumination in the 

 electric light. 2. Different plants are differently affected l)y the 

 light. 



It now remains for us to determine how to avoid or coi'rect the 

 injurious etfects while we still hold to some of the accelerating 

 influences of the light ; and we must also ascertain what plants 

 most readily adapt themselves to such changed conditions of life 

 as the electric light introduces. Both Siemens and Deherain 

 found that ordinary glass cuts off many of the higher refrangible 

 or ultra-violet rays in which the electric spectrum abounds and 

 which are too intense for the welfare of most plants. Common 

 glass has this property in a marked degree, and it cuts off many 

 of these rays in the solar spectrum. In our next experiment, 

 therefore, the injurious portion of the electric light was cut out by 

 a globe surrounding the arc. We first tried an opal or 

 whitened globe, and the light, as before, ran all night. There 

 was at once a marked change. The effect of the modified light 

 was much less evident than that of the naked light. Spinach 

 showed the same tendency to run to seed, but to a much less 

 extent, and the plants were not affected by proximity to the 

 lamp. Radishes were thrifty in the light house, and the leaves 

 did not curl, but they produced less than in the dark house, 

 although the differences were much less marked than in the former 

 experiments. The loss in growth of radishes due to the electric 

 light averaged from one to five per cent in the screened light, 

 while the loss occasioned by the naked light had been from 45 to 

 65 per cent. It was noticeable, also, that while the tops or leaves 

 were lighter under the naked light, they were heavier under the 

 modified light than those of normal plants ; and this is interesting 

 in connection with the fact that lettuce did much better under the 

 modified light than in normal conditions. 



We had now prevented most if not all of the secondary 

 injurious influence of the light due to the ultra-luminous portion 

 of the spectrum, and we had found one plant — the lettuce — 

 which was able to adapt itself completely to the new conditions 

 and, by availing itself of the added light, had been greatly 

 benefited. The other plants were imable to adjust themselves to 

 the accelerated assimilation, and ran too quickly to seed, or 



