feet in a sand-bank, that it is the habit of the maize plant to send out roots twenty feet long. The length depends upon the soil rather more than upon the plant.

It is greatly to be desired that our knowledge of the relative development of the roots of our various crops should be completed. The roots are in one sense the most important part of the plant. We cannot influence a field crop, except through the roots. We do not manure the tops, or operate upon them in any way. All our efforts to promote growth must be directed to the root, and yet we do not know with precision what is the extent and depth of the roots of the wheat plant, for example, as compared with the roots of any other plant. We simply know that some plants have more and longer roots than others; that clover, for instance, is deeper rooted than wheat.

Some important contributions to our knowledge of this subject have been made quite recently, and I have placed upon the blackboard some figures obtained by chemical analysis of the residues of certain crops; i. e., the stubble, and the roots down to the depth of ten inches. At Proskau, in Prussia, there is a Government Agricultural School, and Dr. Weiske, one of the chemists connected with that school, a year ago last summer, measured off certain plots of land, several yards in dimensions, and carefully excavated the soil to the depth of ten inches and with extreme pains dug out all the roots he could get in that depth of soil. These he dried, weighed, and analysed, and these figures show the average of his results, calculated in pounds upon the surface of an acre. Unfortunately, he did not state anything about the quantity of the crops; but from the fact of their growing at Proskau, where the soil has long been under cultivation, it is to be presumed that these crops were good.

Composition of Roots and Stubble-lbs. per acre.

The first column gives the amount of vegetable matter which

was contained in the roots and stubble. We are not informed

what the height of the stubble was; probably it was rather short, as straw is too valuable in most parts of Prussia to be left on the ground. These figures were obtained to throw light on what happens under the circumstances that prevail in the culture at Proskau. We want a similar work done to throw light on what happens under our circumstances, and this work should be repeated several years, so that we shall arrive at average figures that can be fully depended upon. Referring to the table, you have of rye stubble and roots, 3400 lbs.; of barley, 1515 lbs.; of oats, 2200 lbs.; of wheat, 2240 lbs., of red clover, 6580 lbs.; of buckwheat, 1630 lbs.; of peas, 2400 lbs.; of lupine, 2800 lbs.

You see at once the bearing of these figures. You see that when you have got your clover hay off the field, there remains, within ten inches of the surface, twice as much vegetable matter as is necessary to go into the next rye crop, and three times as much as is necessary to go into the next wheat crop. That helps

to explain why clover is a good preparation for these crops. Look at the column headed "Nitrogen." In rye, we have 62; in wheat, 22; in clover, 180 lbs. Take lime. In rye, 69; in clover, 246; and so on. What I want to show mainly by this table is expressed in the first column of figures-the amount of vegetable matter remaining in the roots.

Here we have another set of figures which refer somewhat in detail to two of our standard crops-Rye and Clover.

In this experiment, due to Heiden, a mass of soil one foot wide, five feet long, and four feet in depth, was enclosed in boards, then lifted out and the roots removed by careful picking and washing. The average length of the roots was noted, and the total weight of roots and tops ascertained. This was done, as the table shows, at several different periods of growth.

You see from the second column that the roots of rye at the time of heading had an average length of eight inches, and did

not gain anything beyond that. In the clover, at the time of budding, their length was eighteen inches ; in bud, sixteen inches. That looks like going back; but you must remember that the roots measured in the one case were not the same as those measured in the other, but were from another plot of ground. In blossom, they were fourteen and one-half inches; when ripe, fifteen inches. The grand result is simply this: that wherever rye roots were eight inches, clover roots were twice that length; and this in soils which I suppose were quite similar in character. That is a piece of information of great value.

MR. LYMAN. I have heard old men express the opinion that the principal benefit of clover arose from the large amount of root which is left in the ground, even after it is plowed under. I suppose that to be the fact.

PROF. JOHNSON. Undoubtedly so.

MR. LYMAN. If we grow a plant which has a very small root, of course the vegetable matter to supply the succeeding crop is comparatively small.

PROF. JOHNSON. I have heard old farmers, and young ones too, say that they would give more for that part of the clover crop below ground than for the part above ground. You have here an accurate setting forth of the proportions. Look at the figures which represent the weight of the top and of the roots. You see there is a rapid increase in the amount of top in the rye plant-from fifty up to two hundred and fifty; but you observe that the absolute amount of roots diminishes. Whether that is due to any actual decay of the root, or whether to the fact that each result came from a different plot of ground, or because of different care in extricating the roots from the soil, we have no information. It may be due to the fact that there was less development of root in one place than in another.

QUESTION. Might it not be owing to an absorption of the root into the top?

PROF. JOHNSON. It may be. I had supposed that old roots would have the greater absolute weight. If these figures are correct, they are interpreted by your suggestion, which is supported by some observations that have been made regarding the mode of growth of the underground organs.

In the next column of figures we have the ratio of root to top. The root is taken as a fixed quantity, ten. In the case of rye we have, in the first place, 10:17; then 10:45, 10:59, 10:136. In the

case of clover, 10:16, 10:19, 10:23, and lastly 10:15, which may be an error of observation.

Here you have another capital fact brought out-the greater relative quantity of roots in the ripe clover plant. You have half as much roots as top, in the clover plant, whereas you have almost fourteen times as much top as roots in the ripe rye plant. These plants, then, are very different in the way in which they act upon the soil, and therefore in the way in which they leave the soil. When you reap rye close to the ground you take away one hundred and thirty-six out of one hundred and forty-six pounds, and thus leave very little in the soil. When you cut clover you may leave half as much in the ground as you take off. That is a point of great importance in considering their relative bearing upon the question of exhaustion, and shows that you may expect a very different result from leaving clover roots and clover stubble in the soil than from the roots and stubble of rye.

MR. LYMAN. If we cut the rye low we take very nearly the whole of the plant off from the land, and it requires five times as much put back to bring the rye field up to an equality with the clover field, as it stands cut, with the roots in the ground. Therefore we cannot look for a crop that would be equal to what clover would bring us unless we restore this ratio.

MR. LYMAN. What is the difference if we plow the two crops under?

PROF. JOHNSON. The total weight of your rye crop is 272; the total weight of clover is 246; so that in this case the clover has a somewhat less absolute mass of vegetable matter.

QUESTION. There are two or three other important questions. We want to know if the plants take from the soil a certain amount of manurial constituents of saline matter?

PROF. JOHNSON. They do, of course. That is one of the first principles of agriculture.

QUESTION. Do these roots left in the soil create any thing?.
PROF. JOHNSON. Nothing whatever.

QUESTION. Then they take from the soil manures to grow them, the same as what you take off?

PROF. JOHNSON. Certainly. They take manures or equivalent nutritive matters.

QUESTION. It took all these manurial matters to make this crop,

and if you carry it off you carry away those manurial matters; whatever you leave restores what it took to make it, and no more?

PROF. JOHNSON. Yes.

MR. GOULD. Ought it not to be said that in its previous condition the manurial matter was in an insoluble condition, not adapted to the plant; whereas, what you leave is in a soluble condition, and assimilable?

PROF. JOHNSON. During the growth of a crop, plant-food in the soil does pass from an insoluble into a soluble form, and being taken up by the crop remains in that part of the crop left in the field in a state adapted for immediate use. The deep rooted clover also, in this case, brings up, from an average depth of sixteen inches, matter which remains in part within the range of shorter-rooted grain crops.

SECOND LECTURE.

I was speaking yesterday on the peculiarities of plants which enable them to act differently on the stores of nutriment which may be supplied to them in the soil. I spoke of the differences in the absolute quantity of roots which various plants put out into the soil and also of the differences in the depth of roots; and gave some illustrations on those points. I propose to speak this morning of the different structure of the foliage of plants.

We know with absolute certainty that a large share of the feeding of the plant is done through the leaves. We cannot certainly tell how much goes on through the leaves and how much through the roots, in highly manured and very rich soil, but experiments have demonstrated that all the carbon of the plant (which is about fifty per cent. of the weight of the dry plant) may come from the atmosphere; it is not necessary that any of it should come from the soil. The seeds of various agricultural plants-Indian corn, oats, barley, etc.-have yielded a larger increase under artificial circumstances, where the roots had no carbon whatever at their disposal, than is ever produced under field culture. It is a well known fact of agricultural practice, that soils which are nearly destitute of vegetable matter, and therefore have no considerable source of carbon in them, will produce large crops. Some very sandy soils, containing but little carbon, may be made to produce heavy crops by irrigation. Crops are also raised on soils free from organic matter, or from sources of carbon, by the aid of fertilizers which themselves furnish nothing of that sort. Carbon, then, which makes up half of the weight of the dry plant, is