112 



THE FARMER'S MAGAZINE. 



it may depend more on the degree of liquidity than on 

 any discriminating power in the root ; but we are wholly 

 unable to explain that so much greater a portion of 

 water should be absorbed than of the salt held in solu- 

 tion. Saussure concluded that it does not so much de- 

 pend on the earths which constitute the soil, as on the 

 quantity of earths held in solution by the liquid part of 

 it. So that earthy and saline matters existing in the 

 soil, and being always found in plants, wc can scarcely 

 help considering them as a substancs necessary to the 

 growth of plants ; but without manures, no earths, 

 salts, air, or water will support their proper growth. 

 Giobert mixed four earths— silica, alumina, lime, and 

 magnesia— in proportions to constitute a fertile soil, and 

 supplied the plants growing in them with water ; but 

 none grew till he applied water from a dung-hill. 

 Lauipadius planted vegetables in one pure earth, and 

 supplied them with dung-hill water ; they grew and con- 

 tained the usual earthy matters, notwithstanding the 

 total absence of any of them in the soil. Plants have 

 been resolved by chemical analysis, but no satisfactory 

 conclusions as to what substances they derive from the 

 earth as nourishment can be drawn from a knowledge 

 of the constituent parts of organization. If a plant be 

 strongly heated in a close vessel, allowing only smoke 

 to escape, the residue is always the same, and is called 

 charcoal or carbon by the chemists ; of this carbona- 

 ceous matter a considerable quantity is always found in 

 garden-moulds and in rich lands, derived no doubt from 

 the remains of vegetable substances of which the mould 

 was originally formed. It is insoluble in water, and 

 cannot enter in that state into plants ; hence we may 

 suppose that it is rendered acceptable to their pores by 

 a variety of changes and combinations. Vegetable 

 mould is a loose black mass, obtained from plants putri- 

 fied in the open air without any mixture of animal 

 matter ; it causes plants to grow with great vigour, and 

 must contain or constitute of itself a great source of 

 nutriment. New countries owe their fertility to this 

 substance. When exposed to continued cultivation it is 

 dissipated, and the soil is impoverished. Two hundred 

 grains of oak mould distilled, and the same quantity of 

 undecayed oak, gave as under : 



Mould. Oak. 



Inches (Fr.) 



124 IIG 



34 2D 



Grains (Fr.) 



Carburetted hydrogen gas 

 Carbonic acid 



Water containing pyrolignate of am- 

 monia..... 53 80 



Einpyreumatic oil ]0 13 



Charcoal 51 4\^ 



Ashes 8 Oi 



Mould, and the vegetables from which it is derived, 

 give nearly the same results ; but mould contains more 

 charcoal than the vegetables, and more ammonia, and 

 consequently more azote. 



Plants contain but few elements in their construction 

 and organization, and are chiefly composed of charcoal 

 and aeriform matter. They give, by distillation, vola- 

 tile compounds, of which the elements are pure air, in- 

 flammable air, coaly matter, and azote, or that elastic 

 substance which forms a great part of the atmosphere, 



and is incapable of supporting combustion. They de- 

 rive these elements either by their leaves from the air, 

 or by their roots from the soil ; and the sap, which nou- 

 rishes the plant, and is finally converted into substance, 

 in order to add to its bulk by extension of parts, is de- 

 rived from water or from the fluids of the soil, and is 

 altered by, and combined with, principles derived from 

 the atmosphere. The principles of vegetable matter 

 contained by manures from organized substances are, 

 during putrefaction, rendered either soluble in water or 

 ceriform ; and in these states they are capable of being 

 assimilated to the vegetable organs. No one principle 

 affords the pabulum of vegetable life: it is neither 

 charcoal uor azote nor hydrogen alone, nor oxygen, but 

 all of them together, in various states and combinations 

 CDavyJ. 



The fixed alkalies consist of pure air and highly 

 inflammable metallic substances ; but there is no reason 

 to suppose that they are resolved into their elements, in 

 any of the processes of vegetation. 



Elastic fluids are by some thought to constitute the 

 chief food of plants, and the principal cause of the fer- 

 tility of soils. Carbon, being the only fixed ingredient 

 in plants, is insoluble in water or in the acids of the 

 soil, and only in combination with azote and oxygen. 

 Heat is very favourable, as without its agency no sub- 

 stance can assume the gaseous forms. 



Oils have also been supposed to enter into the food 

 of plants, as some oily productions are found to be 

 great improvers of land ; but oils are not miscible with 

 water, and must suppose the presence in the soil of lime, 

 chalk, marl, or soap-ashes, to convert them into a 

 transmissible state. 



The earths are not convertible into the elements of 

 organized compounds — carbon, hydrogen, and azote. 

 They consume very small quantities of earth, found in 

 their ashes, and are not converted into new products. 

 They give hardness and firmness to the organization in 

 an epidermis of siliceous earth, and strengthen and pro- 

 tect it from the attacks of insects and of parasitical 

 plants. Soils and their bases, the metals with oxygen, 

 are not altered in vegetation : they may be corrected by 

 a modification of their earthy constituents, by probably 

 affording a better receptacle for the absorption, reten- 

 tion, and giving oft' of moisture, and the means of useful 

 and fertilizing combinations. 



Experiments have been quoted to showthat the soilsex- 

 erted a powerful influence on the qaulityof metallic oxides 

 contained in the plants; for, though the composition of 

 the ashes differ, the quantity of oxygen contained in all 

 the bases is the same, or an equal number of equivalents 

 of metallic oxides. And hence the opinion has been 

 entertained, that plants do not produce any inorganic 

 substances, alkalies, or metallic oxides. 



Carbonaceous matter, in all active manures, must be 

 in a state of combination soluble in water ; and lime 

 also, pure or in a state of salt. Magnesia and alumina 

 may be rendered so by means of carbonic-acid gas ; and 

 silica may be dissolved in water : and though we cannot 

 comprehend the different changes and combinations, we 

 may conclude water to be the prime agent. The pro- 



