ELEMENTS or AGRICULTURE. 
48 
LESION VIII. 
THE FORMATION OF HUMUS, AND ITS PROPERTIES. 
55. Humus results from the decomposition of organic 
bodies (see No. 8). The proportion and nature of its con¬ 
stituent elements are not always the same; for in some 
cases animal, in others vegetable parts predominate. 
56. Straw, and the excrements of cattle, are destined to 
be transformed into humus. As this substance is of an 
earthy texture, gardeners give it the name of mould. This 
last denomination, however, has also been given to the 
manure derived from the cleaning of ditches and the sweep¬ 
ings of streets, that have been exposed for a time, in heaps, 
to the action of the atmosphere. 
57. Among the bodies forming humus, some are decom¬ 
posed in the open air, others in the bosom of the earth, and 
others in wet and marshy places, according to the circum¬ 
stances in which they may have happened to be placed. 
In the latter case, turf is often formed. This proceeds 
from the decomposition of vegetables that have grown 
successively, for a long time, upon the remains of plants 
similar to themselves. 
58. Turf, or peaty lands, ire recognised by their elas¬ 
ticity, their porosity,* and their blackish color. Turf is 
employed as fuel, and as manure. Turf formed under the 
water is devoid of any acid principle ; but that on the sur¬ 
face of the soil is often acid. 
59. The properties of humus vary according to the 
* Elasticity and porosity are properties possessed by all bodies in a greater 
or less degree. When a body submitted to pressure bends out, and resumes 
its first shape after the pressure is taken off, it is said to be elastic. A 
sponge, for instance, is elastic. Porosity is a property possessed by bodies 
of being filled with holes, of a greater or less size, and more or less numer¬ 
ous. Thus, the human skin is very porous, as a square inch of it is pierced 
wick many thousand holes. 
