are given upon the blackboard. At present a fair commercial price for

The rectified guano, to which your attention has been called, contains, in one ton of 2,000 pounds,—

A single ton of this is sold for $69.00, which is in close proximity to its true value. I place as high an estimate upon the value of the reduced phosphoric acid as upon the soluble, but it is usually regarded as less valuable, and is put at about six cents instead of ten. Whatever you are able to save from the above prices in purchasing and preparing your own fertilizers is so much to your advantage. The cost of the soluble phosphoric acid in the superphosphate, which is to be made in your presence to-day, will be a trifle over 7 cents per pound, and this arises from the low prices of the raw materials used. Bone charcoal at $20 per ton, and oil of vitriol at $35, make the resultant superphosphate cost about $25 per ton, not estimating labor. Estimating the soluble phosphoric acid it contains at ten cents, the allowable value, and it is worth over $35 per ton. In the purchase of raw materials the quality and price are always to be considered, and the cheapest sources of supply are to be investigated.

SOILS AND THE GROWTH OF PLANTS.

BY PROF. LEVI STOCKBRIDGE, OF MASSACHUSETTS.

I apprehend that the expression "exhausted soil" is often used with little precision of meaning, and sometimes, perhaps, in ignorance of what constitutes the real difference between exhaustion and fertility. There is an important sense in which an exhausted soil is an impossibility. Plants are made up out of the material of the soil. Nearly all the soil, from its surface down to the bed-rock, however deep the mass may be, is capable, in answer to the action of natural law, of being transformed from the soil-form to the plant-form: therefore we cannot say that the soil is exhausted until the entire mass has passed through this transformation. Yet we have acres and acres of land which we know a hundred years ago were fertile; but today, although in its aggregate and in its general physical characteristics and appearance it remains as of old, it is, nevertheless, very sterile. There must, therefore, be a very marked distinction between soil in general, and fertility. Mr. A. owns large areas, leagues of land; and yet he possesses nothing of which he can immediately avail himself for the production of crops. And, again, Mr. B. is the owner of a very small area; but he owns something which will enable him at once to harvest the most bountiful crops.

Now, there is a great distinction, as I have already said, between soil and fertility. The question which I am to discuss this afternoon is really this difference between these two conditions of the land; and I shall necessarily be obliged, in discussing it, to speak somewhat of the composition and organism of plants, the composition and the changes of soil by which soil is

converted into plants; and then, again, I must speak of the influence of the air and of the water in producing these changes, and the influence of the general growth of plants to the same end.

First, the plant. To me the living plant is always a wonder; to me there is something within the living, growing plant that is a profound mystery. And yet there is an aspect of this case in which we may say the plant is as well known as the building, in its structure and in its composition, is to the mechanic who has just erected it. The seed is to me a wonder, and it is to me, also, in some aspects, a profound mystery. Curious and wonderful is its formation. It is composed of two principal parts: first, the germ, which is a little plantlet, or more properly a plant in embryo, composed of roots, of stem, of bud, and of leaves. This is also surrounded by a little sack of cellular material, prepared by the parent plant as the food of the young plantlet before its own organs are able to gather food from the element in which it is located. Now the mystery of the thing is, that this little plantlet enclosed within the endosperm of the seed has within it the vital principle. It is alive, and, though apparently a dead thing, it will live on year after year, until there shall be a conjunction of all those circumstances which produce germination; and then it starts into active life.

Now, we go to work, and deposit this seed in the warm, moist soil. From the water of the soil it absorbs moisture, and expands. The oxygen of the air and the warmth cause this cellular mass, which we call the endosperm, to rot. It decays, it is taken to pieces (so far as the cellular mass is concerned), and separated into its constituent parts, dissolving in water; and then circulation and growth begin by the formation of cells, expansion takes place, cell is added to cell, cell to cell, until finally the organs by which the plant can supply its own food being developed, and the endosperm exhausted, it grows on with continued additions, enlarging, expanding, sending out new organs. And, if it be an annual plant, it throws out its blossom, perfects its seed, and dies; but if it be a perennial, like the acorn for instance, it makes its annual growth, enlarging and expanding year after year, and century after century, until finally the magnificent old oak of the forest stands before us, often of many tons

weight. Now, then, in both these instances there has been a very large accumulation of matter from some source or other; but, mark you, there has been no new creation. The matter which was gathered and massed into this plant was matter as old as the morn of creation, and it has been simply passed through certain changes, been used by nature simply to build up the organism. But what is the matter? Whence is it? Those are the questions. for us to answer.

Examine, now, this plant. Take the oak, if you please, to which I have alluded. Examine it with the naked eye; examine it under the microscope: and what do you find? Nothing that you ever saw before. There is nothing in it, nothing disclosed by the most powerful microscopic lens that you ever saw in the soil. Could it have come from the soil? No soil particles are visible; nothing that resembles the soil with which you have always been familiar. We are at a loss to know what it is. Supposing we bring in the chemist to make an examination, and he shall analyze this plant by fire, putting oxygen to work upon it, and we find by quick combustion that we have reduced it from its original condition; and now, if we were simply to weigh the ash, we should have in our crucible two pounds in weight out of every hundred of which the oak was originally constituted. Ninety-eight parts out of every hundred have taken on an invisible form, and disappeared. We have found nothing that resembles soil.

Go a single step further, and ask the chemist to take what we call the "ash," and apply his tests, and tell us what material it is, and whence it is. Applying his chemical tests to the ash, the chemist tells us, "Here is silica, here is potash, here is lime, soda, magnesia, phosphoric acid, sulphuric acid, chlorine, iron." We have not reached our point yet. Neither you nor I ever knew lime as lime in the soil; we never knew potash as potash in the soil. Although we are familiar with all these elements in the arts, yet we have never found them in the soil; and the question comes back, Whence this material that the plant has found which we call "ash"? And therefore we go to the soil, and see if we can find it there. A casual examination of the soil discloses this first. cellular material that seems to

Here is a mass of fibrous and be in a decomposing or broken

down condition. That, we conclude at once, must be the decaying materials which have come from the former growth of plants. Further than that, we find under the microscope that this soil is made up of small, broken, sometimes rounded, sometimes angular pieces of rock, similar to the rocks which are in our fields and in the country around us,-pieces of quartz, pieces of granite, of micaceous and talcose rocks, and of limestone rocks; but still we do not find anything like what we find in our crucible and call it ash.

Further careful examination discloses the fact that these particles of rock of which our soil is composed are distinct minerals. Here we find talc, we find mica, we find hornblende, we find felspar, we find calcite, magnesite, apatite, and phosphorite; but we have found neither lime, nor potash, nor soda, nor magnesia, nor anything which we find in the ash: we find simply distinct, well known minerals. Call on the chemist again. What says he? All these minerals are distinct, well known chemical compounds. They are not only particles of minerals which constitute rocks, but they are, away back and behind all that, distinct, well known chemical compounds. They are a union of silica, more generally of silicic acid, with lime, potash, soda, phosphoric acid, sulphuric acid, chlorine, &c. Now, then, we find at last that in a chemical form we have in the soil precisely the same materials that we find in the ash of the plant which we burned; and it is possible that although these minerals are as indestructible as the rocks, yet it is possible that this plant, somehow or other, contrived a way to draw lime, potash, and phosphoric acid out of the rocky materials of the soil. us, then, go back to the plant, and commence another examination.

The feeding organs of the plant, we read, are the leaves and the roots. We will examine first the leaves. Now this leaf is curiously and wonderfully made. First, it has a frame-work, which we call the ribs of the leaf. Through the centre, comparatively speaking, is one large timber, made of curiously compacted fibrous material, connected with the stem of the leaf, and by the stem with the cambium of the plant from which it grows; branching out on the right hand and the left are ribs or timbers of smaller dimensions, strongly built in all directions;