CHAPTER II. 
MANURES AND THEIR APPLICATION. 
The theory of manures, and the practical application of 
them, is intimately connected with the knowledge of the 
composition of plants and of soils. 
The vegetable organic constituents are composed chiefly 
of Carbon, Oxygen, Hydrogen, and Nitrogen. The organic 
compounds, denominated non-nitrogenous, are important 
constituents of all plants. Some of them such as cellulose, 
liquine, starch, gum, sugar and oily matters, are universally 
diffused over the vegetable kingdom. 
Carbon enters largely into the composition of plants; it 
is said to form two-thirds of the weight of dried plants in 
general. This substance is familar to us in the form of 
charcoal. Charcoal is porous, and has the power of absorbing 
soluble gases in large quantity, and of separating saline and 
other matters from solutions. 
Nitrogen enters into combination with Hydrogen and 
forms Ammonia, composed of 1 equivalent of Nitrogen and 3 
of Hydrogen. Ammonia is absorbed by the soil, and may 
thus be rendered available for the use of plants; clay attract- 
ing and retaining Ammonia. Part of the Nitrogen of plants 
is also derived from Nitric Acid and Nitrates. In order that 
nitrogenous matter may be formed, plants must havea supply, 
not only of Nitrogen, but also of Sulphur and Phosphates. 
