136 POPULAB EBEOES. 



grows in the night, while we all know that in per- 

 petual darkness, as in a cellar, growth, though it 

 may be rapid, is only at the expense of material 

 previously formed. The following additional ex- 

 periments on the effect of lights of different color 

 on vegetation are quoted in the Horticulturist for 

 1872, page 153: 



" Mr. Best has studied the influence of light, 

 heat and color on vegetation. In order to test 

 the effect of green light on the sensitiveness of 

 the Mimosa, he placed several plants under bell- 

 glasses of different color, set in a warm green 

 house. At the end of a few hours a difference 

 was already apparent. Those subjected to green, 

 yellow, or red light had the petioles erect, and the 

 leaflets expanded; the blue and the violet, on the 

 other hand, had the petioles almost horizontal, and 

 the leaflets hanging down. In a week those placed 

 beneath blackened glass were already less sensi- 

 tive; in twelve days they were dead or dying. 

 From that time the green ones were entirely insen- 

 sitive, and in four days more were dead. At this 

 time the plants under the other glasses were per- 

 fectly healthy and sensitive; but there was a great 

 inequality of development among them. The 

 white had made great progress, the red less, the 

 yellow a little less still ; the violet and the blue did 

 not appear to have grown at all. After sixteen 



