mation of the country, but they are in reality the result of chemical differences, or of differences of materials that enter into the soils, and which determine the trees that grow upon it. So with crops; if you select any soil and undertake to grow plants there, for a time they will grow well, just in proportion as the soil contains what the plant requires in greater or less abundance. If it requires a particular substance in large quantities, the continual growth of it will exhaust the soil. Let me explain this word exhaust. Suppose you plant green crops, as the potato, for years in succession, without adding anything to the soil, if the crops are large, you will take a large quantity of potash, particularly from the soil; besides taking out a portion of other matters belonging to the soil, it selects this potash in large quantities. After cropping for a long time, the land will cease to grow the potato, because of the exhaustion of the potash. This is what is called special exhaustion, that is, there may be enough of other substances left to grow the potato. Hence, in many instances, the addition of wood ash has been found to be a simple mode of making the soil grow the potato. Now, suppose in a case of exhaustion, that you introduce a crop that contains or requires but little potash or much phosphoric acid and alternate this crop with the root crops, it is obvious that the soil will hold out longer, because in that case, you do not draw so constantly on any one substance in the soil. This is one reason for the rotation of crops, and the most skilful rotation is that which is governed by these rules. Thus you see the meaning of the two terms, general and special exhaustion. Land is generally exhausted where this alternation is pursued for a long series of years, and will remain so until all those things are added which have been taken from it, in sufficient quantities to feed the plant. If I grow one crop continually, and that crop requires one thing to be present in the soil in large quantities, I exhaust it of that one thing only, and I can add that and restore the soil, if I know what that is. This is the great object of the researches and labors of science in this direction-a kind of labor requiring more study than you can well understand at a glance. The great object is to understand what a plant takes from the soil and what to put in to bring it back again.

Prof. J. illustrated this point by showing that a system of cropping might be adopted, which would lead to a partial exhaustion of the soil, and which it was vain to try to bring back again by ordinary manure, but which could be easily restored, and without any great expense, by applying to the soil, the substances which must have been taken from it by that system of cropping. Let me draw your attention, said he, to a fact familiar to you, in this country where there is little intercourse with the large towns, and where the farmer raises or

makes everything at home-his soap, candles, &c. In making soap for instance, you know that the wood ash is essential; but the farmer, whom I have described, does not take the ash of soft wood, but of hard wood; he will tell you, that his reason is, that there is no potash in the ash of pine, and so it is in reality. Prof. J. went on to state the quantity of potash contained in the ash of different woods, adding, that the ash of those trees which contain most potash, is the ash of those which grow in soils where there is an abundant supply of potash. Tobacco is a crop that contains much mineral matter. Suppose an acre to yield 800 lbs. of tobacco. These 800 lbs. contain about 160 lbs. of mineral matter, which is carried off as it were, by this kind of crop, and which will ultimately exhaust the soil specially. You may think it remarkable, that in the rotation of crops, first, wheat, then turnips, then barley, then clover, then wheat again, a very common rotation, mineral matter may be carried off to the extent of 1300 lbs. per acre, you would naturally suppose that this would exhaust it more than tobacco, which in 4 years carries off 600 lbs. per acre; but here is the difference we do not sell off the straw; we return that to the land in the form of manure, and by this means, the yearly loss is confined to that which is contained in the grain; the grain contains only 83 lbs. for 4 years; whereas tobacco carries off 600. Of course, tobacco exhausts the soil far sooner; that, I repeat, is special exhaustion, and knowing what tobacco carries off, we can supply it.

One other ob

• We give an analysis, taken from Prof. Johnston's lectures, 2d edition, of the ash of the tobacco leaf, and the composition of a special manure for tobacco:

All the ingredients which are necessary to replace 100 lbs. of the ash of tobacco leaves, are present in the following mixture:

servation, as to the particular operation of this. You see how a knowledge of what the plant takes from the soil, is necessary to know what is the nature of exhaustion, and what to put into the soil to bring it back again so far as mineral matter is concerned. The organic matter plays an important part in the growth of plants, but I do not speak of that now. But you see how a knowledge of the inorganic substances taken out by a series of crops enables us to show what to put in. But it does more; it enables us to prepare manure which shall contain all the mineral matters that the crops have taken out, and to make special manures adapted to special cases. I have prepared tables of special manures thus adapted, in order to restore to the soil what the crops have taken from it. This is important, for it points out how to manufacture what a farmer wants to promote the growth of any crop. and to restore land to fertility which has been exhausted. I do not pursue this matter further. I think I have shown you illustrations enough to satisfy you of the value of the application of refined chemical research to the plant, and, that though complicated, they have a practical bearing on the every day business of the farmer, and to show you how many kindred branches of science have been actually brought to bear directly upon the pecuniary profit of his pursuit.

At our next meeting I shall show you how science has been brought to bear on the rearing and feeding of stock, and shall present to you considerations on this topic which can scarcely fail to interest you; and you will then see that this wide field of science, over which the practical farmer may travel with advantage, becomes wider and wider with every step that he takes.

LECTURE SEVENTH.

RELATIONS OF CHEMICAL PHYSIOLOGY TO THE ANIMAL-ITS FOOD AND ITS GROWTH.

GENTLEMEN: The subject which I propose to introduce this evening is an exceedingly wide one, as indeed I may say of all the subjects of which I have treated. At the same time, I think the points I shall be able to present this evening are so plain and intelligible that you can see plainly the width of the subjects of which I treat. You will recollect that at our last meeting I presented to you the composition of the elementary part of the plant; and I showed you, that if you take any part of a plant and burn it, that by far the largest portion burns away; that the part that burns away consists of four elementary substances, carbon, hydrogen, oxygen, and nitrogen. These three last being dif ferent kinds of air. I showed you, also, how they differed and how. they were to be distinguished. It is necessary to re-introduce this, to make you acquainted with what is called the ultimate composition of the organic parts of plants, animals and soils. I wish to make use of these words, and unless previously explained you would not be able to follow them. First, I draw your attention, not to the elementary constituents of plants, but to the substances that exist in the plants which we eat; for example, the great mass of this rod consists of woody fibre; then, if you take a grain of ground wheat you know that it contains much starch; that is another substance that the plant produces. The sugar cane produces sugar; this sugar exists in all plants. These substances all consist of the elementary bodies spoken of. There is no nitrogen in these I mention, but others contain it. Now, of the crops we cultivate these three substances, woody fibre, starch and sugar constitute a very large proportion. But before I show you of what they consist, and in what proportions, I must explain to you the nature of the important substances existing in the plants which we cultivate for food.

If you take a quantity of wheat flour and make it into a dough, and ut this dough on a piece of muslin, tied over a glass and pour water

on it, the water will pass through the muslin in a milky form. If you continue the process until the water passes through quite clear, a substance will remain, which the chemists call gluten. The milky substance which passes through the muslin, falls to the bottom in the shape of a white powder-that is starch-thus I separate wheat flour into starch and gluten. Now, this gluten contains all four of the elementary bodies I have named-it contains about 16 per cent of nitrogen-hence the nitrogen in the atmosphere is of great importance in the growth of wheat. Take any vegetable substance-the straw of wheat or of this piece of wood; and it contains a great quantity of fibrous substance called woody fibre-that exists in all plants. If you take this gluten and put it into spirits of wine and heat it, you can extract from it a quantity of oil. So with Indian corn, or oats, and from the stalk and straw of either you can extract more or less oil. We have then, first of all, the woody fibre, we have starch, and gluten, and oil; these four are important to the nourishment of animals and exist in all plants. But before showing the importance of these substances to the growing animal, I must show you the proportions in which they exists.

Average composition of 100 parts of the more common grains roots, and grasses, &c.

Some of the above numbers, are approximations, only, especially the fatty matter, which is very uncertain, and the buckwheat.

This table contains all we know of the composition of crops, you see that there is water in all this food. Wheat contains 15 per cent of water, the turnip from 88 to 90 per cent-showing the For an analysis of Indian corn, by J. H. Salisbury. see Transactions of 1848,

p. 678.