and from that, it can abstract those substances which are termed elementary; but over the vital principle it exerts no control, and of its nature it takes no cognizance. Whenever, therefore, the terms chemical, electro-chemical, or the like, occur in this volume, as applied to the organs or functions of living plants, they are to be viewed as subordinate to the energy of the vital principle. Language fails in points of such deep import, and modesty compels us to avow our ignorance.

"In studying the functions of vegetable being," says the late Sir James Edward Smith, in his Introduction, "we must constantly remember that it is not merely a collection of tubes or vessels holding different fluids, but that it is endowed with life, and consequently able not only to imbibe particular fluids, but to alter their nature according to certain laws; that is, to form peculiar secretions: this is the exclusive property of a living being. Animals secrete milk and fat from food which has no resemblance to those substances; so, vegetables secrete gum, sugar, and various resinous substances from the uniform juices of the earth, or perhaps from mere water and air. The most different and discordant fluids, separated only by the finest film or membrane, are kept perfectly distinct while life remains; but no sooner does the vital principle depart, than secretion, as well as the due separation of what has been secreted, are both at an end, and the principle of dissolution reigns absolute."

SECTION I.

SCIENCE OF GARDENING.

PART I.

NATURE AND OFFICES OF EARTHS AND SOILS.

1. Earths and Soils being the laboratory wherein the food or nutriment of the plant is prepared, and the media through which it is conveyed to the roots; it becomes a matter of primary importance to the gardener and agriculturist, to obtain correct ideas of their component parts, and of the offices which they perform in the work of vegetation. It will also be very useful to acquire a method of general classification, so as to arrive at some degree of precision and systematic arrangement: on this subject, says the Encyclopædia of Gardening, at No. 1031. 1. "A correct classification of soils may be founded on the presence or absence of organic or inorganic matter in their basis. This will form two grand classes, viz. primitive soils, or those composed entirely of inorganic matter; and secondary soils, or those composed of organic and inorganic matters in mixture. These classes may be subdivided into orders, founded on the presence or absence of saline, metallic, and carbonic matter. The orders may be subdivided into genera, founded on the prevailing earths, salts, metals, or carbon; the genera into species, founded on their different mixtures; the species into varieties, founded on colour and texture; and subvarieties, founded on moisture, dryness, richness, lightness, &c." In naming the genera, the first thing is to discover the prevailing earth or earths;-" thus Sir Humphry Davy has observed, the term sandy soil should never be applied to any soil that does not contain at least seven-eighths of sand: sandy soils that effervesce with acids should be distinguished by the name of calcareous (chalky) sandy soils, to distinguish them from those that are siliceous," (of the nature of flint.) "The term clayey soil should not be applied to any land which contains less than one-sixth of impalpable earthy matter, not considerably effervescing with acids: the word loam should be limited to soils containing at least one-third of impalpable earthy matter, not considerably effervescing with acids." "In general, the soils, the materials of which are the most various, are those called alluvial, or which have been formed from the depositions of rivers; and these deposits may be designated as siliceous, calcareous, or argillaceous (clayey); and in some cases, the term

saline may be added as a specific distinction, applicable, for example, at the mouths of rivers, where their alluvial remains are overflowed by the sea." The word loam is in the mouth of every one, yet no term is more vague, and less understood; generally speaking, loams may be said to consist of fine siliceous sand to the extent of, at least, one-half; of aluminous earth-combined with, and coloured by oxide of iron-one-third, more or less; and of a small portion of chalk. These constituents will be particularly described hereafter.

2. The Qualities and Value of Soils are discoverable botanically, and by chemical analysis. First, botanically, that is, by the plants which grow on them naturally. "The saintfoin (kedysarum onobrychis) is almost always an indication of a calcareous soil; the common colt's-foot, (tussilago-farfara,) of blue clay; purple sandwort, (arenaria rubra,) of poor sand; the common wood-sorrel, (oralis acetosella,) of the presence of iron." Secondly, by chemical analysis. The quantity of soil best adapted to a perfect analysis is stated to be four hundred grains: it should be collected in dry weather, and exposed to the air till it become dry to the touch. The process of analysis is complicated, and one of extreme nicety. Some cultivators may be qualified to perform the necessary operations, but in general a degree of accuracy is required which can only be obtained by constant practice, founded upon scientific principles. "The following is the analysis of a fertile soil in the neighbourhood of Bristol; in 400 grains, there were of water, 52; siliceous sand, 240; vegetable fibre, 5; vegetable extract, 3; alumine, 48; magnesia, 2; oxide of iron, 14; calcareous earth, 30; loss, 6." On the utility of analysis Dr. Ure (Dict. of Chem.) observes, that "no system can be devised for the improvement of lands independently of experiment; but there are few cases in which the labour of analytic trials will not be amply repaid by the certainty with which they denote the best methods of melioration; and this will particularly happen when the defect of composition is found in the proportions of the primitive earths. In supplying organic matter, a temporary food only is provided for plants, which is in all cases exhausted by means of a certain number of crops; but when a soil is rendered of the best possible constitution and texture with regard to its earthy parts, its fertility may be considered as permanently established. It becomes capable of attracting a very large portion of vegetable nourishment from the atmosphere, and of producing its crops with comparatively little labour and expense."

3. Of the Uses of Earths. Pure earths, "exclusively of organized matter and water, are considered by most physiologists to be of no other use to plants than that of supporting them, or furnish

ing a medium by which they may fix themselves" in a situation favourable to their future growth. "But earths and organic matter, that is, soils, afford at once, support and food." Thus the pure earths may be considered as mechanical agents in the soil. They consist, chiefly, of metallic bases united to oxygen, not readily decomposable; and consequently they cannot be reasonably supposed to be convertible into the elements of organized matter, which, as has been stated, are chiefly found to be oxygen, hydrogen, carbon, and azot. Plants, it is true, consume a small portion of the earths they grow in, as is discoverable by burning, for their ashes are found to contain earths; but the quantity has been ascertained never to equal more than a fiftieth part of the weight of the plant consumed. "The earthy parts of the soil are chiefly useful in detaining water, so as to supply the proper proportions to the roots of the vegetables, and they are likewise efficacious in producing the proper distribution of the animal or vegetable matter." The earths, when duly mixed with such matter, prevent it from decomposing too rapidly, and regulate the supply of its soluble parts in proper proportions to the roots of the plants. The earths are also "necessary to the existence of plants, both as affording them nourishment, and enabling them to fix themselves in such a manner as to obey those laws by which their radicals are kept below the surface, and their leaves exposed to a free atmosphere."

4. The due tenacity and coherence of the soil arise from the finelydivided matters of its constituent parts, "and they possess the power of giving those qualities in the highest degree, when they contain much alumina," (pure clay.) "A small quantity of finely-divided matter is sufficient to fit a soil for the production of turnips and barley; and a tolerable crop of turnips has been produced on a soil containing eleven parts out of twelve sand; a much greater proportion of sand, however, always produces absolute sterility." Tenacity is obtained by certain proportions of finely-divided vegetable and animal decomposable matters in union with alumina.

5. Friability, or looseness of texture, is chiefly occasioned by the admixture of sand, and in a certain degree, this quality is of importance, "in order that the operations of culture may be readily conducted, that moisture may have free access to the fibres of the roots, that heat may be readily conveyed to them, and evaporation may proceed without obstruction." "As alumina possesses all the properties of adhesiveness in an eminent degree, and silex, those of friability, it is obvious that a mixture of those two earths in suitable proportions, would furnish everything wanted to form the most perfect soil as to water and the operations of cultivation. In a

soil so compounded, water will be presented to the roots by capillary attraction; it will be suspended in it, as in a sponge, in a state of minute division, so that every part may be said to be moist, but not wet."

6. "The power of soils to absorb water from the air is much connected with fertility. When this power is great, the plant is supplied with moisture in dry seasons; and the effect of evaporation in the day is counteracted by the absorption of vapour from the atmosphere by the interior parts of the soil during the day, and by both the exterior and interior during the night." "The soils that are most efficient in supplying the plant with water by absorption from the atmosphere, are those in which there is a due admixture of sand, finely-divided clay, and carbonate of lime," (or chalk, which mixture constitutes a loam,) "with some animal and vegetable matter: and which are so light as to be freely penetrated by the atmosphere."

The productiveness of soils is influenced by the nature of the sub-soil on which they rest. When they are immediately situated upon a bed of rock, they are rendered dry by evaporation much sooner than when the sub-soil is of clay or marl. "A clayey subsoil will sometimes be of material advantage to a sandy soil, and will retain moisture so as to be capable of supplying that lost by the earth above." "A sandy or gravelly sub-soil often corrects the imperfection of a too great degree of absorbent power in the true soil. In calcareous countries, where the surface is a species of marl, the soil is often found only a few inches above the limestone, and its fertility is nevertheless unimpaired; though, on a less absorbent soil, this situation would occasion barrenness; and the sandstone and limestone hills in Derbyshire and North Wales may be easily distinguished at a distance, in summer, by the different tints of vegetation. The grass on the sandstone hills usually appears brown and burnt up; that on the limestone hills, flourishing and green."

In the Isle of Thanet, and other districts, where the sub-soil is chalk to a considerable depth, the verdure of the grass, and of young trees and shrubs, is often retained during parching seasons, when in many other situations, the grass is entirely scorched, and the trees lose their leaves, owing to the continuance of dry weather: this was particularly observable in the hot summer of 1818. Chalk absorbs moisture readily, and retains it tenaciously; hence, in hot, dry summers, it gradually affords moisture to the roots of plants at a time when more open and porous soils are comparatively deprived of moisture.

7. Chemical agency of soils. Besides the mechanical uses of soil, there is, according to Sir Humphry Davy, "another agency between