cally, by the roots of the clover plant. The same separation is often attempted when chalk and similar applications are used upon the land. We shall have occasion hereafter to notice these agricultural processes more fully, but it is desirable to realise the fact that the fine state of division in which the earthy matter exists in our clay soils is very frequently in itself a source of difficulty.

In like manner the mechanical condition of many of our sands gives an instance of a difficulty just of the opposite character. Here we often find what is really a collection of minute gritty stones, and in too many cases with little soft earthy matter intermixed with them. The difficulty is increased when this sand consists of fragments of quartz, and being tolerably pure silica, so that it necessitates other matters being added to the soil before it will be in a position to yield any food for plants, for the decomposition of such sand could not yield the necessary food.

But between these two extremes we have a great variety of soils, which have an entirely different mechanical condition. In fact we find large stones, small stones, coarse grit, fine grit, earthy matter, existing in them in a regular gradation. Thus there is often a gradual change of form taking place, according to the tillage operations carried out; whereby the materials of the soil are steadily modifying their mechanical condition, and thereby coming more fully under the influence of chemical agencies. The presence of stony

matter in our soils must not-as a rule-be regarded simply as an encumbrance. It exerts a mechanical influence upon the finer particles of the soil in the manner already stated, favouring the admission of air and moisture into the soil, increasing its friability of character, and in some cases acting as a shield from the sun's rays, at a time when moisture in the soil is of great value. Hence the wisdom shown by many farmers in cracking stones, and leaving them on the land, instead of removing them. There are other considerations which demand attention, especially the relation of these matters to various chemical agencies; but we are here dealing with the mechanical influences which are called into operation.

The fine or coarse state of division in which the particles of the soil exist has another important influence, to which attention has already been directed. Such is the power exerted by the soil in bringing up a supply of water into the land to a greater height than the general water level. Most persons have noticed water being placed in the saucer in which a flower-pot may be standing, and they have seen that it has been drawn up into the soil in the pot. The natural tendency of the water was to remain at the low level, and hence in such cases it must be drawn up to a higher level by some other power. This power is largely dependent upon the mechanical division of the soil. It is known that if a fine glass tube be placed in water, we have the water adhering to the side of the tube by a surface attrac

tion, and it rises above the level of the water in the glass. The smaller the tube the greater the height to which it rises, and this action is especially observable when the tubes are so fine as to be of a hairlike character. For this reason these tubes have been called capillary tubes, and the power by which the water is raised is known as capillary attraction. This power is possessed by soils very much in proportion to the fineness of the particles of which it is composed, for passages are formed between these particles of a larger or smaller size, according to the finer or coarser condition of the soil. The mechanical condition of the soil in this way very materially influences this supply of water to the growing crop, which is especially valuable in excessively hot weather. When the soil contains decaying vegetable matter, this also favours the capillary powers of the land.

Closely connected with this power is the ability of the soil to hold water. It has been shown that

lbs.

lbs.

100 of sand commenced dropping when it had received 25 of water. 100 of Loam

40

Thus the power of holding water increases with an increase in the fineness of the particles of the soil. It thus corresponds very closely with the capillary powers of the soil, even if it be not due to the same influence.

The power of absorbing moisture from the

F

atmosphere is possessed by soils in somewhat corresponding proportions, thus :

lbs.

lbs.

1000 of Sand in 12 hours of the night gained 2

So that in this respect also the power of absorbing moisture from the atmosphere steadily increases with the increasing fine condition of the particles of the soil.

The possession of these powers naturally increases the productive character of land, somewhat in the proportion in which these powers operate, and it is curious to notice that there appears to be some connection between these mechanical conditions and the rental value of land. For instance

lbs.

1000 of Bagshot Soil, worth (say 4s. or 5s.) per acre

lbs.

16

18

1000 of Fertile Soil from Somerset,

1000 of very Fertile Soil from E, Lothian

But whilst we recognise this influence of the mechanical structure of the soil, as contributing towards its fertility, it is equally necessary to regard it as only one of the causes of fertility. It is probable that many peaty soils of low productive power possess each and all of these powers in a higher degree than any of the soils which were

experimented upon. That these powers are of great practical value, in their influence upon the productive powers of the soil, has been clearly established; but we shall hereafter have occasion to show that a variety of circumstances contribute their respective shares to the work to be accomplished, and render it desirable that each and all of these agencies should be carefully taken into account.

CHAPTER XIII.

IT is probable that a proper appreciation of the influence of the mechanical condition of the soil upon its productive powers, is one of the points of management in which a good farmer excels. As a matter of fact, it is equally important to take care that the soil shall be in such a state as will enable plants to search after their food, and to receive it in a healthy condition, as it is to provide that food. It has already been shown that fertilising materials are not of necessity plant-food, because they may be present in an insoluble condition. But even after they have taken a form in which they are ready for the use of the plant, the mechanical condition of the soil often interferes with the efforts of the growing crop to secure its food. We have therefore not only to secure the presence of the materials necessary for plant-growth, and to have those materials in an available form, but we must