32 THE VIIAL I UNCnONS. 



portion of the water, which was not exhaled by 

 the leaves, has been actually decomposed,* and 

 that its separated elements, the oxygen and the 

 hydrogen, have been combined with certain pro- 

 portions of carbon, hydrogen, nitrogen,-]" and various 

 earths, metals, and salts, so as to form the proxi- 

 mate vegetable products, which are found in the 

 returning sap. 



The simplest, and generally the most abundant 

 of these products, is that which is called Gum. 

 From the universal presence of this substance in 

 the vegetable juices, and more especially in the 

 returning sap of all known plants, from its bland 

 and unirritating qualities, from its great solubility 

 in water, and from the facility with which other 

 vegetable products are convertible into this product. 

 Gum may be fairly assumed to be the principal 

 basis of vegetable nutriment : and its simple and 

 definite composition points it out as being the 

 immediate result of the chemical changes which 

 the sap experiences in the leaves. During the 



* Boussingault was led to this result by a careful and elaborate 

 series of experiments, by which he has proved that plants contain 

 a hydrogenated substance, containing a proportionate quantity of 

 hydrogen three times greater than that which is requisite to form 

 water with the oxygen present. In ordinary cases, the quantity of 

 hvdrogen which is thus assimilated varies from 0..5 to 2. per cent. — 

 Annales des Sciences Naturelles, serie ^2, xi. 31. 



t It also appears, from Boussingault's researches, that plants in 

 full vegetation abstract nitrogen from the atmosphere, and assimi- 

 late it into their system. A much larger quantity is thus obtained 

 and appropriated by those plants, such as clover, which may be 

 advantageously ploughed into the soil, than by the cerealia, the 

 cultivation of which impoverishes the land, because they derive 

 their azote almost exclusively from the organic substances it con- 

 tains. — Ibid. X. 257. 



