CHAP, ii.] of Plants. DC Saussure. 497 



instructive to observe how he tries to decide whether the 

 nitrates, sulphates and ammonia, which are found in the sap of 

 plants, are introduced from without, or are formed in them 

 from their constituent elements ; he concludes finally that the 

 former is the more probable opinion. That the greater part at 

 least of the carbon of plants comes from the atmosphere could 

 scarcely be a matter of doubt with those who knew the writings 

 of Ingen-Houss ; but Senebier devotes special attention to this 

 question ; he endeavours to take all the co-operating factors 

 into the calculation, and especially to prove once more that the 

 oxygen given off from the plant in light comes from the carbon 

 dioxide which has been absorbed, that the green parts only 

 and no others are able to effect this decomposition, and that 

 there is a sufficiency of carbon dioxide in nature to supply the 

 food of plants. But although he convinced himself that green 

 leaves decompose the carbon dioxide which surrounds them in 

 a gaseous form, he supposed that it is chiefly through the roots 

 that this substance finds its way with the ascending sap into 

 the leaves, and this view often gave occasion to further error in 

 later writers. 



The tedious prolixity of Senebier's book was one reason 

 why it never enjoyed the measure of appreciation and influence 

 which it deserved ; but it was also thrown into the shade by 

 the appearance of a work of superior excellence, distinguished 

 at once by the importance of its contents, by condensation of 

 style, and by perspicuity of thought. This work was the 

 ' Recherches chimiques sur la vegetation ' of THEODORE DE 

 SAUSSURE 1 (1804), which contained new observations and new 



1 Nicolas Theodore de Saussure was born at Geneva in 1767, and died 

 there in 1845. He was the son of the famous explorer of the Alps, and 

 assisted his father in his observations on Mont Blanc and the Coldu Geant. 

 In 1797 he wrote his treatise on carbonic acid in its relation to vegetation, 

 a prelude to his ' Recherches chimiques ' ; the latter work received great 

 attention from the scientific world, and he was made a corresponding 

 member of the French Institute. He was a man of literary tastes, and took 



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