A. Because the deeper the soil is made, the deeper the roots can go in search of food.

Q. Can you give me any other reason?

A. Yes, when my drains are so deep I can go down 20 or 22 inches with my subsoil-plough without any risk of injuring them.

Q. Does draining serve any other purpose besides that of carrying off the water from the land?

A. Yes, it lets in the air to the subsoil, and allows the rain-water to sink down and wash out of it any thing which may be hurtful to the roots of plants. Q. Do such hurtful substances often collect in the subsoil ?

A. Yes, very often, and crops which look well at first, often droop or fail altogether when their roots get down to the hurtful matter.

The teacher may illustrate this answer by referring to the layers of iron-ochre, or pan, which in many districts, are met with,—and to such curious facts as that observed in the East of Fife, where the beans and oats, which look well up to April or May, often blacken and fail in June or July, when the roots get down to the ochrey subsoil. It is the local saying when this happens-that the beans or oats have gone to Auchtermuchty—a fair being held there about the time when the beans usually fail.

Q. Why are many of the heaviest clays in the country laid down to permanent pasture?

A. Because the expense of ploughing and working these soils is so great, that the value of the corn reaped from them is not sufficient to pay the farmer for his trouble.

Q. How could these heavy clay lands be rendered lighter and more cheap to work?

A. By draining, subsoil ploughing, and by the addition of lime or marl when it is required.

The teacher will here explain to his pupils the difference between common ploughing, which merely turns over the surface soil,-subsoil ploughing, which only stirs and loosens the subsoil,—and trench ploughing or trenching, which brings the subsoil to the surface.

Q. Would the land after this treatment also give greater crops of corn?

A. Yes, not only would it be more cheaply worked, but it would yield a greater number of bushels of wheat an acre than before.

Q. Would this increase be sufficient to pay the cost of draining?

A. Yes, the cost of draining clay lands is generally paid back in three, or, at the utmost, in five, years, and the crops still continue greater than before.

V. OF THE INORGANIC FOOD OF PLANTS.

Q. What are the purposes served by the inorganic part of the soil?

A. The inorganic or earthy part of the soil serves two purposes; first, it serves as a medium, in which the roots can fix themselves, so as to keep the plant in an upright position; and, second, it supplies the plant with inorganic food.

Q. The inorganic part of the soil consists chiefly of sand, clay, and lime; does it contain no other substances?

A. Yes, it contains small quantities of eight or nine other substances.

Q. Name these substances?

A. Potash, soda, magnesia, oxide of iron, oxide of

manganese, sulphuric acid, phosphoric acid, chlo

rine.

Q. Are not these the same substances which exist in the ash or inorganic part of plants?

A. Yes, the same substances exactly-only they form a much larger proportion of the soil than they generally do of plants.

Q. Do you understand, then, where plants obtain all the inorganic matters they contain?

A. Yes, they obtain them from the soil only. Q. Why can they not obtain them from the air? A. Because potash, soda, magnesia, &c. do not exist in the air.

Q. How does this earthy matter enter into the plant?

A. It enters by the roots.

Q. In what state?

A. In a state of solution. The rain and spring waters dissolve them and carry them into the roots.

Here the teacher will explain the meaning of the new words dissolve and solution—showing how salt and sugar melt away or dissolve in water, forming clear solutions of salt or sugar in which these substances can be recognized only by the sense of taste-but from which they may again be obtained unchanged by boiling off the

water.

Q. Do all soils contain every one of the inorganic substances, potash, soda, lime, &c. which you have mentioned?

A. All fertile or productive soils do.

Q. Why must a fertile soil contain them all? A. Because plants require them all for their healthy growth.

Q. Do plants require them all in equal proportion?

A. No. Plants must have a certain small quantity of each of them, but they require more of some substances than of others.

The teacher may illustrate this question by directing the attention of his pupils to the following table, which he should cause to be copied upon a large piece of calico, and hung upon the wall of his school-room. He can thus readily point out, that, while 1000 lbs. of red clover hay leave 75 lbs. of ash, there are present in this ash 28 lbs. of lime, but only 20 lbs of potash, and less than 4 lbs. of magnesia, and so on with the ash of the other kinds of hay mentioned in the table.

Quantity of ash left by 1000 lbs. of hay from

This table will suggest to the teacher many instructive questions-which his pupils will readily understand and answer, when they have the table hanging before them.

Q. Are those substances which are present in the plant in such minute quantities really necessary to its growth?

Ă. They appear to be all equally necessary—just

as the few ounces of nails or glue are as necessary to the joiner in making a box, as the many pounds of wood which the box contains.

Q. Suppose a soil to be entirely destitute of some one of these substances, what would happen? A. Good crops would not grow upon it.

Q. Suppose it to contain a large supply of all the others, but only a small supply of some one or two of these substances, what would happen?

A. Those plants would grow well upon it which require only a small quantity of these two substances, but those which require a large quantity of them would be stunted and unhealthy.

Q. Give me an example.

A. If the land contained little lime, it might grow a good crop of rye-grass, and yet not be able to grow a good crop of lucerne.

By referring to the above table the teacher may exercise the understanding of his pupils by asking for other examples of a similar kind, which the intelligent boy will readily give by considering the numbers on the table. Thus he may say lucerne requires more phosphoric acid than rye-grass does; therefore if there be little phosphoric acid in the soil lucerne will not grow so well upon it as rye-grass would do. Other tables of a similar kind also the teacher may make use of, which he will find in the author's" Elements," and especially in his "Lectures on Agricultural Chemistry and Geology."

Q. Suppose a soil to be destitute of a considerable number of these different inorganic substances,what would happen?

A. It would refuse to grow good crops of any kind whatever. It would be naturally barren.

Q. Are any soils known to exist which are naturally barren or naturally fertile ?