WITH REFERENCE TO HORTICULTURE. 5 



held in suspension by water, and deposited in plains, or along the 

 hanks of rivers, along with organic matter also held in suspension. 

 The earthy character of this soil must necessarily always partake of 

 the character of the rocks of the country in which it is found. 



Peat or bog is composed of partially decayed vegetable matter, 

 soft, light, and spongy to the touch ; and is the very reverse of sand 

 with respect to water, holding that element like a sponge, so as, in its 

 natural state, to be totally unfit for the growth of vegetables, except 

 those of a very low grade. 



The organic matter in soils in its solid state may be considered as 

 carbon, which is found pure in the diamond, and tolerably so in the 

 charcoal of wood. In soils it is found in various states of decompo- 

 sition, from recent woody fibre to humus, which is woody fibre in a 

 state of decay. The proportion of organic matter varies exceedingly in 

 different soils. In barren sands there is scarcely a trace of it, while in 

 fertile soils it varies from 10 to 30 per cent. ; and peat- bogs which have 

 been drained and cultivated contain often 80 or 90 per cent. Humus, 

 according to Professor Liebig, exercises its influence on vegetation " by 

 being a continued source of carbonic acid, which it emits slowly. An 

 atmosphere of carbonic acid, formed at the expense of the oxygen of 

 the air, surrounds every particle of decaying humus. The cultivation 

 of land, by stirring and loosening the soil, causes a free and unob- 

 structed access of air. An atmosphere of carbonic acid is, therefore, 

 contained in every fertile soil, and is the first and most important 

 food for the young plants which grow in it. The property of humus, 

 or woody fibre, to attract from the surrounding air its carbonic acid, 

 diminishes in proportion as its decay advances ; and at last a certain 

 quantity of a brown coaly-looking substance remains, in which this 

 property is entirely wanting. This substance is called mould ; it is 

 the product of the complete decay of woody fibre, and constitutes the 

 principal part of brown coal and peat." (* Organic Chemistry,' p. 47.) 

 For practical purposes, all the soils ordinarily met with may be 

 reduced to the following : 



Loose naked sands or gravels, without either clay or calcareous 

 matter, and almost destitute of vegetation on the surface ; exemplified 

 on some parts of the sea-shore, and on Hounslow and other extensive 

 heaths. 



Calcareous soils or gravels, containing little or no clay or organic 

 matter, and almost without vegetation on the surface ; found on the 

 sea-shore in some places, and on the surface of chalky districts. 



Loams. Rich sandy loams consist of sand, clay, and more or less of 

 calcareous soil, with organic matter ; they never become hard on the 

 surface after rains followed by drought, and never retain water to such 

 an extent as to prove injurious to vegetation. Vegetation commences 

 Mme weeks earlier in sandy loams than in clayey loams, in the same 

 climate, or even in the same garden ; and during summer, plants on 

 such soils will be in advance of those on clays; so much so, as Mr. 

 Lymburn has observed, as to attain maturity a month earlier. Clayey 



