PROPERTIES OF HUMUS. 



CHAPTER II. 

 THE ORIGIN AND ASSIMILATION OF CARBON. 



Composition of Humus. 



Some virgin soils, such as those of America, contain vegetable 

 matter in large proportion ; and as these have been found emi- 

 nently adapted for the cultivation of most plants, the organic 

 matter contained in them has naturally been recognised as the 

 cause of their fertility.* To this matter, the term " vegetable 

 mould " or humus has been applied. Indeed, this peculiar sub- 

 stance appears to play such an important part in the phenomena 

 of vegetation, that vegetable physiologists have been induced to 

 ascribe the fertility of every soil to its presence. It is believed 

 by many to be the principal nutriment of plants, and is supposed 

 to be extracted by them from the soil in which they grow. It 

 is a product of the putrefaction and decay of vegetable matter. 



The humus, to which allusion has been made, is described by 

 chemists as a brown substance easily soluble in alkalies, but only 

 slightly so in water, and produced during the decomposition of 

 vegetable matters by the action of acids or alkalies. It has, 

 however, received various names, according to the different ex- 

 ternal characters and chemical properties which it presents. 

 Thus, ulmin, humic acid, coal of humus, and hufiiin, are names 



* When the weight of the soluble parts of this vegetable matter is com- 

 pared with that of the plants growing upon t, it is seen that only a very 

 small part of their substance could have been procured through its agency. 

 Thil is the case even in the most fertile soils. — (Saussure, Richerche* 

 sur la VigHation. 



