THE INFLUENCE OF LIGHT ON LIFE. 237 



We shall now consider what would take place if a plant were 

 kept continually in light, or if it received a great deal more light 

 than the normal quantity. As we cannot very well, ourselves, 

 perform an experiment to prove what happens, we must borrow 

 from Professor Stokes. Three pots of mustard-seed were sown at 

 the same time. One was kept under the usual conditions of day- 

 light by day and darkness by night ; another was kept in darkness 

 during the day and was exposed to the electric light during the 

 night. At the end of the experiment the plants in these two pots 

 were found to be much alike. The third pot, however, was 

 exposed to daylight during the day and to the electric light during 

 the night. At the end of the experiments the plants in this pot 

 were found to be stouter looking, to have larger leaves, and to be 

 of a darker green than the plants in the other two pots, but they 

 were not so tall. We gather from this experiment that the plants 

 in the third pot were hastened forward by having gathered into a 

 short space of time an aqiount of light which, in the ordinary 

 course of things, would have been spread over a much longer 

 period. 



Professor Bailey, an American, has recently been making 

 numerous experiments as to the influence of the electric light upon 

 plants, and he has found that when plants were kept under con- 

 tinuous light — that is, sunlight by day and electric light by night — 

 growth was expedited. In the case of some cabbages grown under 

 these conditions, maturity was reached about two weeks before 

 others which were cultivated under the usual conditions. It was 

 also observed that if plants were placed too near the electric light 

 it proved very injurious to them. The electric light contains 

 certain rays which are harmful to vegetation, but it has been proved 

 that this injurious property may be avoided to a great extent by 

 passing the light through transparent glass. These experiments 

 show that the electric light affects different plants in different ways, 

 but that the general result is a hastening of the growth. Such an 

 unnatural state of things, however, must surely prove injurious to 

 the plant if continued for very long without a sufficient period of 

 rest or darkness being allowed. 



Dr. Carpenter tells us that the same annual plant, in arriving 

 at its full development, requires everywhere the same amount of 



