Dr Gardner on the Action of Light on Vegetables. 79 



three-fourths high, in the case of turnips, were most sensitive ; 

 indeed these plants were found to give the best results, and 

 were used almost exclusively after the first month. 



The spectrum was allowed to fall on the specimens at a dis- 

 tance of fifteen feet from the prism, and undecomposed light 

 shut out by screens. Each ray acted in a separate compart- 

 ment, unless otherwise stated. 



(9.) The following extract of an experiment, will shew 

 some farther details : — 



" August 13. — Five jars, containing each about one hundred 

 turnip seedlings, were placed respectively in the orange, yel- 

 low, blue, indigo, and violet rays, at 9 h. A.M. Day bright ; tem- 

 perature in shade at noon 80° Fah., in the sun 95°. Duration 

 of sunshine G^ hours. Result at 3^ p.m. The third column 

 of the table shews the altitude of the plants at the commence- 

 ment of the observation : 



" August 14. — The same plants, with the addition of a fresh 

 crop (6) in the green ray. Exposure from 9 a.m. to 3 p.m., or 

 six hours sunshine. Temperature in shade at noon 85° Fah. 

 and 105° in the sun. Result at 3 p.m. 



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

 cluded after 80 hours, of which 12J were sunshine, and 17J 



* The fifth column contains a comparative estimate of the depth of 

 colour, assuming unity of the highest value ; on this scale the plant in blue 

 light did not become green, and the value is negative, but there was a 

 visible alteration designated olive, and indicating the tint which vegetables 

 assume in passing from the yellow colour of darkness to green. 



