ON VEGETABLE EESPIRATION. 166 



of the attempt of M. Daguerre to produce the picture of a landscape 

 in its natural colours; " for," says M. Dumas, "the chenoiical rays, 

 essential to the Daguerian phenomena, have disappeared, ; and being 

 absorbed by the leaf are kept in reserve for .the enormous expenditure 

 of chemical power necessary to decompose so stubborn a substance as 

 carbonic acid. " 



In addition to carbon, vegetables absorb also hydrogen by decom- 

 posing the water about their roots ; this has been proved by M. M. 

 Edwards, Colin, and Boussingault. According to the experiments 

 of the latter chemist, they also fix a minute quantity of azote. 



The following table is a concise recapitulation of the phenomena 

 of vegetable respiration :— 



VEGETABLE RESPIBATION. 

 Ist coloured f During day'\ 



The essential phenomena of vegetable respiration diffar entirely 

 from those presented by the respiration of animals : the first diffuse 

 oxygen, that beneficent supporter of life, whilst the second, on 

 the contrary, contaminate the atmosphere by the impure mix- 

 ture of carbonic acid ; thus vegetables are employed in puri- 

 fying the air which has been vitiated by animal respiration. Some 

 other observations may also be adduced in support of this principle. 

 It is well known that a great number of vegetables are produced 

 under the sea which form by their combination, a sort of verdant 

 carpet beneath its waters. M. De Humboldt remarks, when the 

 waters of the sea are penetrated by the solar rays the fish appear 

 vigorous and full of life ;» on the contrary, they are dull and lan- 

 guid when these rays are absent, and when the sun remains a long 

 time clouded they seem as if ready to die. Struck with this fact, 

 the illustrious observer analysed a little sea water during the sun- 



