52 ELEMENTS OF AGRICULTURE 
4. That a soil should be productive, it must contain ne 
mineralogical elements in suitable proportions. Each one 
of the simple bodies (silica, clay, lime, etc.) that we have 
described, is sterile in itself; it is only by their mixture 
that they can give the soil the qualities suited to vegeta¬ 
tion. 
5. If Nature has not always effected these mixtures in 
just proportions (and this is one reason of the difference in 
the value of land), she furnishes us, in return, the means 
of amelioration, that enable the farmer to supply this de¬ 
fect.- It is precisely because the use of fertilizing means 
is neglected, that we see everywhere so much waste land. 
6. The soil requires two species of elements that it is 
important not to compound. Some accrue from organic 
bodies, and are called manures ; their principal object is 
to serve as food for plants. The others are the produce, 
for the most part, of the mineral kingdom, and take the 
name of ameliorators ; they give the earth advantageous 
properties relative to cultivation, by improving its texture 
when either too stiff or too loose. 
7. There are also other substances, such as plaster, 
which in most cases, without modifying the composition 
of the soil, give activity to the vegetation of plants, by 
forcing them to absorb more nourishment from the soil 
and atmosphere. These bodies are called stimulants. 
8. The same substance may perform more than one 
function ; it may serve at the same time as a manure and 
as an ameliorator. Dung, for instance, as we shall see 
hereafter, applied to certain soils, may at the same time 
furnish food to plants and force into action certain inert 
principles contained in the soil 
9. It is of the utmost importance to the success of the 
farmer, that he should give his attention to soils that are 
deficient in their composition; but above all things he 
sh uld be acquainted with the mode of action, and the 
