produced under water in marshy districts are soils of the same kind, but infertile. The further relations which exist between the soils.composed of the most diverse mixtures of these chief ingredients, and vegetation, as also between the latter and water, air and heat, are included in the following Sections. EXAMINATION OF SOILS. I shall only offer a few short remarks here, since the farmer can seldom be in a position to institute especial researches and to carry the results obtained into useful application in even isolated cases. What is the proportion of the finer earthy particles to the coarser? How much water can the soil absorb? How much organic matter (humus) does it contain? Has it acid properties? What amount of carbonate of lime does it contain? These are about the most important questions in practice. The farmer may answer them in the following way, if not quite accurately, still in a simple and easy manner. One quarter of a pound of the earth dried and powdered must be boiled for a short time in about a pint of water, until the lumps have sunk into a uniform mass; the whole is then to be emptied into a plate. A strip of blue litmus paper soaked a little while in this mass will show whether the soil contains acid humus; in such case the blue colour of the paper changes to red. Such a soil demands manuring with lime. The earth must next be well stirred up with a stick, and more water added to it. After a short time the thick creamy liquid must be poured off, but with care, so that the sand, which on account of its greater weight sinks to the bottom first, may not flow over with the liquid. The residue is to be stirred up with fresh water, and this poured off after the sand has settled. This alternate addition and pouring off of water must be continued until all the clayey, loamy and other fine earthy particles have been washed out of the sand. The sand must then be set aside in the plate in a warm place, and when thoroughly dry, weighed. The dif ference between its weight and the original 4 lb. is to be reckoned as loam, or "fine earthy substance." It is important to ascertain the nature of the sand and its chief ingredients mineralogically. To discover the power of holding moisture, lb. of earth, dried and rubbed to powder, may be shaken into a tumbler, this weighed, and enough water poured on to cover the earth. After twenty-four hours' soaking the supernatant water must be poured off by carefully inclining the glass, and the latter again weighed when no more water runs off. The increased weight gives the amount of water which is retained by the earth, from which therefore may be judged the behaviour of the earth in wet seasons, which however the farmer's practical sense will beforehand enable him to estimate with tolerable correctness. Light kinds of soil will retain 2 to 3 ounces, heavy 4 to 5 ounces, soils rich in humus still more water, in this test. The amount of humus may be ascertained approximatively by heating lb. of strongly dried earth for an hour, in an iron or black-lead crucible, over charcoal; the organic matters are then burned off and calculated from the loss of weight: 1 to 2 drachms (Apoth. w.) loss correspond, in this test, to a moderate proportion of humus, 3 to 4 to a rich, 5 to 6 to humous soils, and quantities above that to humus and peat soils. In rough testing for lime the earth is moistened with a little water and some hydrochloric (muriatic) acid added; if a perceptible effervescence then takes place, we may assume at least a per-centage of lime to exist in it. If we wish to know the amount of lime more accurately, 6 oz. of water and oz. of hydrochloric acid must be poured upon 1 oz. of the earth, the mixture left for an hour in a warm place, and then solution of ammonia (spirits of hartshorn) added, stirring the mass actively all the time, until there is a permanent pungent odour. The liquid must then be filtered through several folds of white blotting paper. The lime is then contained in the clear fluid, and may be precipitated (together with the magnesia) as a white mud, by adding solution of potash; the precipitate is then to be collected on a paper filter, washed, dried and weighed. In most cases, especially in comparative researches, a sufficient average result may be obtained by allowing the fluids to which solution of potash has been added to stand in glass vessels, and comparing the quantities of lime-mud deposited in the different. glasses. The classification of soils I think I may pass over lightly here, since I could only state what has been established by practice from agricultural experience, and is given in detail in agricultural works. Agricultural chemistry is not yet in a position to furnish any addition or improvement worth naming. XVII. THE SOIL AND THE GROWTH OF THE SOIL AS THE HABITATION OF PLANTS. EVERY soil is capable of bearing plants. Left to itself it would become clothed with a carpet of vegetation over the whole earth, provided the two universal conditions of growth of plants, heat and water, were not deficient. Only where these are wanting, in the eternal ice of the polar regions and lofty mountains, and in the waterless solitudes of the sand-deserts, does the earth remain naked and bare, and devoid of vegetation. Even when the soil is covered deeply with water, it does not cease to be a dwelling-place for plants, although these are of different organization from our land plants. Thus sea-weeds rise from the bottom of the ocean, not unfrequently attaining a length of 300 feet and more. And in what is termed the Sargasso-sea or gulfweed bed, is found a tract in mid-ocean, which is densely overgrown with marine plants, and occupies a surface exceeding from six to seven times that of all Germany. But in regard to degree of fertility, which one soil displays beyond another, very great diversities are met with, especially when man, not content with the spontaneous produce of the soil, forces it to bring forth particular kinds of plants, and these in greater abundance. While one soil proves very favourable to the growth of such cultivated plants, and richly repays the care employed in tilling and sowing it, another furnishes but a scanty product, or is quite sterile, that is relatively, for this particular plant. That it is not absolutely sterile is proved by the fact that it may become covered with other plants, if left uncultivated, though these may be of undesirable kinds, namely what are called weeds. We will in the first place make a summary examination, in these two classes of soils, of what "external or physical properties" the soil must have, as an abode for plants, to develope them freely and strongly; and, on the other hand, what properties render it unproductive of cultivated plants. The latter, the sterile kinds of soil, take precedence. 1. UNPRODUCTIVE SOILS. The chief causes rendering a soil unfit for agricultural or forest plants (land plants) may be traced up to a "too much" and a "too little." Too much or too little water, too much or too little heat, and too much or too little access of air, may coincide in their effect, namely, make a soil sterile. If these properties are caused by the geographical position and the climate of a country, of course human force is not in a position to find a remedy. In isolated cases this may be done, if local conditions of the former allow it, for example, by planting or felling forests, by irrigation or draining, and the like; still more frequently, in agricultural practice, if the composition of the soil is the cause of those extreme properties. To change this fundamentally will certainly only be possible under especially favourable circumstances; on the other hand, as experience has repeatedly taught, a wellcontrived treatment and cultivation of the land will produce at least an extraordinary amelioration of the unfavourable conditions of the soil. The indicated causes rendering the soils unfitted for culture by its external character, may be arranged under the two following heads: a. A soil may be unproductive because it possesses too great cohesion, that is, is too stiff and tenacious. Dense clay, such as potter's clay, appears totally unsuited for the growth of plants, because it is too close and solid both in the dry and the wet condition, because it absorbs too much water and holds it too long, because it will not allow enough air to penetrate, and because it is too slowly and too little warmed. In like manner, also, a soil composed solely of finely divided lime or of muddy humous substance, may be totally unproductive, if washed down by rain into a dense compact mass, or when dried up into solidly caked crusts or lumps. Under certain circumstances, especially with a light surface-soil and a damp situation, heavy earths of this kind may even render an otherwise good soil unproductive, if they form the sub-soil, and as such prevent the sinking away of water, so as to give rise to swampiness or sourness. In like b. A soil may be unproductive because it has not sufficient cohesion, that is, is too coarse, loose and open. Pure gravelly, flinty or sandy soils are equally totally unsuited for the growth of plants, because they hold too little water and give this up again too readily, because they become heated too strongly, and because the air has too free access to them. manner, a soil composed solely of porous, loose, fragmentary remains of plants more or less converted into humus, may prove unproductive; as also a calcareous soil in which the particles of lime do not form a pulverulent mass, but are in the form of finer or coarser granules or fragments. c. For the sake of connectedness, it may be further pointed out here, that a soil may become unproductive through excess or deficiency of soluble nutriment, either of organic or inorganic kind, as also through noxious or poisonous substances. Too much of dissolved humous ingredients and salts (for example, common salt, alum, green vitriol, &c.) interfere with the growth of plants, indeed may completely arrest it; in a still far more destructive manner, of course, if they are salts which we have seen to be direct foes of vegetable life, such, for instance, as salts of lead, of copper, &c. The cases of this kind, however, are rare. Very common, on the contrary, nay of daily occurrence, are the opposite cases, where the want of soluble and easily decomposed humous ingredients and salts, if it does not totally remove the productiveness of cultivated ground, at all events evidently diminishes it. These very important cases form the contrast to the following Section. 2. PRODUCTIVE SOILS. The foregoing remarks in themselves indicate the requisitions to be fulfilled to place a soil in a condition to bring forth fruit abundantly. It must-and this is the first and principal necessity— |