from the soil more from the most contiguous layers of earth than from those at a distance. Since rape, from this very peculiarity, must receive a very powerful, in particular a strongly nitrogenous manuring, to make it flourish, of which it only consumes what it can reach in the vicinity, a considerable portion of the manure remains in the soil, the benefit of which comes to the next crop. The general fact of experience, that wheat, &c. flourishes so excellently after oil-plants, may be perhaps chiefly explicable by this cir

cumstance.

Oats are distinguished among the corn-plants by an excessively rich development of lateral roots, which they send out in all directions; hence they are capable of gathering food enough even from a deteriorated and exhausted soil, in which barley, which has far fewer lateral roots, cannot draw up as much nutriment as it requires for its vigorous growth. It must be added, however, that oats can also absorb more food from the atmosphere than barley, since the leaves remain longer fresh, green and active, than those of the latter.

The depth to which a plant sends its roots down into the subsoil, is likewise certainly not without influence on the exhaustion of soil, since this will of course occur later, especially in regard to mineral substances, where a plant can avail itself of the lower layers of soil, than where it is restricted to a more shallow bed. The weight, however, which has been attached to the difference in this respect occurring among our cultivated plants, for the explanation of the different degrees of exhaustion of soil, has greatly diminished by recent researches, according to which the "shallow-rooting" corn-plants send down their fine absorbent roots to a depth of 3 or 4 feet into the subsoil in easily penetrable ground, while those of the "deep-rooting" clover diminish so rapidly with the depth, that it can scarcely be supposed they consume or loosen the subsoil to any considerable extent. In regard to lucerne, on the contrary, there can be no doubt of such a beneficial double effect upon the subsoil being produced.

Collecting once more into a few maxims what we have learnt on the separate facts mentioned; these may be stated, in full agreement with that which I have placed at the com mencement of this discussion, somewhat as follows:

a. The amelioration of a soil sown with clover or similar plants, depends upon the same causes and takes place in the same way as that of shaded and protected soil in forests. Clover sown with corn acts at first like underwood, afterwards as a well-covered plantation.

b. In the first place, plants of this kind absorb so much nourishment, namely carbonic acid, ammonia and water, from the atmosphere, that the roots and other residue produced thereby, remaining on the land at the harvest, give the soil more humous constituents and nitrogen than they have extracted from it during their growth.

c. In the next place the plants act as protectors of the soil, inasmuch as their thick covering of leaves prevents the useless volatilization of the products of decomposition of humus.

d. Finally, both by the permanent shade and the great ramification of the roots, they impart to the soil the crumbling, soft, ripe (yahre) consistence, which experience has shown to be the most favourable to growth of plants, a consistence, in which the weathering and solution of the mineral substances in the soil go on very rapidly.

The same explanations apply also to the beneficial effects which the farmer can produce through green fallows, through under-dunging, and through occasionally laying down light and poor soils to grass.

3. Enrichment through exaltation and regulation of the

activity of soil.

Here we may include all the measures by means of which the farmer endeavours to bring his fields into such outward or physical order, that their relations to water, air and heat shall be those most advantageous to plants; such as improvement of the composition of the soil, tillage and drainage.

Improvement of the composition of the soil has been mentioned already; the endeavour here is to render too tenacious soils looser and mellower, too loose soils more coherent and denser, too wet soils more permeable, too dry soils more retentive of moisture, too cold warmer, too hot soils cooler, &c. Through such ameliorations, among which are marling, laying in mould, manuring with mud, artificial flooding (warping), &c., the soil is generally rendered absolutely richer in nutriment for plants. But even if this is not the case, it will certainly

behave like one become richer, after such an amelioration. Too light a soil is to be compared with a spendthrift; too heavy a soil with a miser; the first makes away with more than his means allow, the second less; by the ameliorations indicated is attained the medium between these two, a wise frugality.

It is equally unnecessary to dwell longer on the different operations of tillage, such as ploughing, hoeing, harrowing, grubbing, rolling, subsoil-ploughing, autumn-ploughing, trench ing, and the like. In all these operations the purpose is the same, namely, to give the soil the proper granulation and loosening most advantageous to the roots of plants, and to restore this when lost; as to the importance of which, all that is necessary has been said already at the beginning of this Section and previously. The more deeply the loosening penetrates the soil, the richer is this made for the plants; when a layer of soil 12 inches thick is opened and made available to these, we give them twice as much of moisture, indeed even more, as when we afford them only a six-inch layer of a soil twice as rich. Ploughing one inch deeper may readily render disposable a store of mineral substances for 50 or 100 crops. The great advantages which experience has shown to result from loosening the subsoil, and from the weathering thereby produced in the soil earth, are sufficiently well known. An exactly similar action results from what is called the black fallow, found so useful in very heavy and refractory soils, by means of which soils of this kind are opened to the vivifying influence of air, heat and moisture, and stimulated to a more rapid weathering and crumbling down. It need scarcely be mentioned, that in deep cultiva tion the dead soil must not be brought at once to the surface, nor the manures turned to the bottom.

Finally, the great extent to which the fertility of a soil which is kept too wet either by rain, springs, standing water or floods, can be increased by draining, has only become properly understood quite recently, since the simple method of drainage through subterranean clay-pipes has come into use. I have the less to say here on the methods by which this is to be carried out, since the practical details have no relation to chemistry, and at this present time form the topic of the day. However, I shall certainly mention briefly the

principal alterations which the soil undergoes through the removal of its stagnant water. These are:

a. Wet soil becomes drier. All our cultivated plants are land-plants, and these require for vigorous growth a soil in which moisture is present, but not in the liquid form as standing water. If the latter is the case, the roots can only penetrate the earth to the depth at which the water stands; at the same time water and marsh-plants make their appearance and displace the land-plants.

b. Some soil becomes too mellow, because air enters the soil where the water has previously been, and makes the same humus produced by 'putrefaction,' decay into too soft a state.

c. Cold soil becomes warmer, for it now receives the full benefit of the heat of the sun and air, while previously a great part of this was expended in the evaporation of water. and could not produce a heating effect.

d. Heavy soil becomes looser, more crumbling and softer; when it dries finer cracks are formed than in the undrained tenacious soils, and it is more easily worked.

e. Sluggish soil becomes more active and powerful, for, by becoming more open and warmer, the two great natural processes by which the food for plants is prepared and rendered soluble, weathering and decay, proceed more rapidly and actively, and to a greater depth down in it. Hence the same quantity of a manure gives a higher effect on drained than on undrained soil.

f. Finally, soil also becomes more certain. As is evident, the farmer by draining changes an uncertain and less fertile into a more certain and far more productive, grateful soil, and renders it to a certain degree independent of the weather, inasmuch as he carries away harmlessly those extremes to which the inhabitants of the northern hemisphere are most commonly exposed. The dread that the rain and snow-water would wash the manure out of the soil and rob it of its soluble nutriment, in filtering through the earth, has proved quite unfounded in deep draining.

That forests also are brought into an incomparably more vigorous growth by the removal of stagnant water, is abundantly proved by experience, and is self-evident after what has been said above, since our finest trees are land-plants,

and their growth is connected with the same conditions of vegetation as that of the cultivated plants of agriculture. That voices are still heard here and there against the draining of marshy soil in forests, resting their arguments on climatic, meteorological, hydrographic and other vain alarms, only manifests an ignorance of Natural Science. If we can place a plantation where a swamp was before, it is certain that the climate, productiveness and the store of water of a district, will not be deteriorated, but rather far ameliorated.

XX. WATER, AIR, HEAT AND LIGHT IN THEIR RELATIONS TO SOIL AND VEGETATION.

THE three ancient elements, water, air and fire (heat and light), constitute the fundamental conditions, giving the fourth old element, the earth, the power of sustaining vegetation; at the same time the principal factors of climate and weather, which determine the greater or less vigour of the growth of plants upon the globe. An indivi dual is only able to exercise a small dominion over these, in very limited and isolated cases; he must take what they offer him; but the prolonged action of whole nations is capable of changing the conditions of moisture and heat of great tracts of country to such an extent, that the work of the fathers may be a blessing or a curse upon their children and their children's children.

Water.

Water covers three-fourths of the surface of the globe as ocean, partly in a solid condition, as at the extreme north, partly fluid, as in all warmer regions; it flows through the land in all directions in the form of rivers; it ascends into the air as vapour, forms clouds there, and falls again to the earth as rain, snow or dew. This everlasting circulation of "water," produced by "heat," is the especial agent which