SOO EFFECTS OP COLOURED LIGHT. 



149, that glass of different colours exercise very different 

 effects upon the plants exposed to the rays of solar light 

 passing through it; that both the exhalation and absorption 

 of moisture by plants, so far as they depend upon the influence 

 of light, are affected in the greatest degree by the most 

 luminous rays, and that all the functions of the vegetable 

 economy, which are owing to the presence of this agent, foUow 

 in that respect the same law. In these experiments it was 

 ascertained that the glass employed admitted the passage of 

 the rays of light in the following proportions : — 



Transparent. Orange. 

 Luminous rays 7 6 



Calorific rays 7 6 



Chemical rays 7 4 



M. Decaisne found, during some experiments to ascertain 

 the effect of light in causing the production of colouring matter 

 in the Madder plant, that when the lower parts of a plant 

 were enclosed in cases glazed at the side with transparent 

 green, red, or yellow glass, the leaves and stem of the part 

 surrounded by red glass, became pallid, and exhibited signs of 

 suffering in a greater degree than under the other colours, but 

 all were affected more or less.* {Recherches sur la Garance, p. 23.) 



Many ingenious experiments of a similar nature have been 

 made by Mr. Hunt as has been already stated (p. 338). But we 

 have not ground at present to believe that they possess practical 

 value. No advantage seems to have resulted from glazing the 

 great Palm House at Kew with green glass of a tint selected by 

 Mr. Hunt himself; and, in short, we have every reason to 

 conclude that the white light which is natural to plants is that 

 which is best adapted to their constitution ; nothing more being 

 required of the gardener than to moderate or increase its 

 intensity. 



Full details respecting the experiments of Mr. Hunt will be found in 

 the Gardeners' Chronicle for 1847, p. 524, and for 1848, pp. 138, 155. 

 In the same work for 1845, p. 55, are also recorded Zantedeschi's 

 ohservations upon the influence of coloured light. 



* The nature of these experiments has been misapprehended in the translation, by 

 Mr. Francis, of Meyen's Report on Vegetable Physiology for 1837, p. 51. 



