254 AZOTE IN PLANTS. 



falls not much bolow that proportion. According to Professor 

 Liebig, the whole of the carbon in plants is derived, through their 

 leaves, from the atmosphere ; and Boussingault, whose authority I 

 respect much more highly, says : a From all we have seen up to 

 this time, we feel authorized to conclude that the greater proportion, 

 if not the whole, of the carbon which enters into the composition 

 of vegetables, is derived from the atmosphere. " (p. 42.) All other 

 chemical authorities concur in maintaining that at least much the 

 larger part of the carbon received by and fixed in plants, is taken 

 from the atmosphere through the leaves. How very great, then, 

 must be the proportion of vegetable nutriment and support, and of 

 materials for growth and increase, derived exclusively from the air ! 

 For it is not only that nearly half their quantity is thus obtained 

 in their carbon alone, and they also take up from water, whether 

 in the air or in the soil, nearly as much as of carbon, in hydrogen 

 and oxygen ; which, though always present in enormous siaper- 

 abundance, cannot be thus used by plants, except in strict propor- 

 tion to the carbon assimilated. All these quantities, then, which 

 the atmosphere supplies either exclusively, or may supply, as in 

 regard to water, probably amount always to full four-fifths of the 

 substance of all vegetable products; leaving but one-fifth, at most, 

 to be derived from 'the soil, or having any direct dependence on the 

 condition of fertility of the soil. 



Further : of this small proportion of vegetable growth and sub- 

 stance derived from and dependent on the contents of the soil 

 say one-fifth, at most, and generally not more than one-tenth part 

 a quantity which varies much in different plants, but on an 

 average making more than half of this proportion derived from the 

 soil alone, consists of inorganic elements ; while the remainder, of 

 about 1 to 4 per cent, only of the whole plant, is of azote, which 

 is either wholly or principally a part of the matter derived from 

 the contents of the soil. (See Table on p. 244.) Yet is this very 

 small supply of azote all-important to the support and product of 

 plants ; and its being duly supplied in organic manures, or other- 

 wise, is the great and essential operation of all improvement of 

 crops through the improvement of soils. In considering, then, the 

 value of azote, we must take care not to measure its importance by 

 its always small quantity in soils, manures, or plants, but by the 

 great and essential operation of this element, and which even in 

 this small quantity it produces. Azote is eminently the enriching 

 part of all putrescent manures, and of all vegetable products serv- 

 ing as food for animals. The most enriching of animal manures 

 abound most in azote ; and, above all, the excrements of carnivorous 

 animals, whose food is also rich in azote. Next in order^stand the 

 excrements of animals fed on the most highly azotized vegetable 

 food. Vegetable matters, compared to animal, in general have but 



