206 APPLICATION OF PRINCIPLES. 



by the most luminous rays ; and that all the functions 

 of the vegetable economy, which are owing to the 

 presence of this agent, follow 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 : 



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 inclosed in cases 

 glazed at the side with transparent green, red, or yel- 

 low 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.* (Meeker- 

 ches sur la Oarance, p. 23.) 



We, however, require very different experiments 

 from any yet instituted, before we can proceed to draw 

 practical conclusions as to the relative effects upon 

 plants of glass of different colours. We do not know 

 what the effect is of the calorific and chemical ra3'S, 

 and therefore we cannot say what may be the advan- 

 tage or disadvantage of their action upon plants. 

 As, however, the object of the cultivator is to protect 



* The nature of these experiments has been misapprehended in 

 the translation, by Mr. Francis, of Meyen's Report on Vegetable 

 Physiology, for 1837, p. 61. 



