Dr. Gardner on the Action of Light vpon Vegetables. 5 



The leaves of 1 and 2 were developed. Experiment con- 

 cluded after 30 hours, of which 12£ were sunshine, and 17£ 

 darkness. The greater altitude of the plants in the indigo and 

 violet rays — a fact discovered by Morren, is due probably to the 

 slowness of exhalation by vegetables in those colors, an effect 

 not of light, but of heat. In this observation, no result whatso- 

 ever was produced on the original yellow color of the seedlings 

 in the indigo and violet rays. 



(10.) The ensuing table contains the comparable points of six 

 similar experiments. The 1st column gives the number of the 

 observation ; the 2d, the plants used ; the 3d, the number of 

 hours of sunshine ; the 4th, the whole duration of the experi- 

 ment ; and from the 5th to the 13th column, the rays of the spec- 

 trum ; the figures in the last spaces indicate only the order of 

 color in the particular observation. The sign of minus is in- 

 troduced, whenever the effect of the ray was not tested, or the 

 result was defective. 



Table, showing the active and inactive rays of the spectrum, in pro- 

 ducing the green color of plants. 



In experiment 5, the blue ray produced a green color, but the 

 usual effect was a light olive. The indigo, violet, and lavender 

 portions were always inactive, although several observations 

 were continued until the plants faded. 



(11.) Under favorable circumstances it requires a long expo- 

 sure to develope chlorophyl. The shortest period I witnessed 

 was in a crop of turnip seedlings, which required two hours in 

 the centre of the yellow rays, but frequently six or more hours 

 were necessary. In the full sunshine of Virginia, it requires 

 more than one hour to produce the same effect. 



The color acquired is not fugitive. It has been observed, 

 scarcely changed after seventy two hours' darkness, in turnips, 



