am not the only one to hold this belief. Such leakage could easily occur unless great care were taken to guard against it; and some precautions that a trained chemist would naturally take might not be thought of by a trained watchmaker. I am assured, further, that the verdict of the committee of the Academy was secured through a fraud. This fraud consisted in the substitution, during the night previous to one of the latest visits of the committee, of more healthy and vigorous plants for the feeble ones which had grown in the case, and which showed by their appearance that they were suffering for want of some constituent of their natural food; and as they had been supplied with everything but combined nitrogen, it is reasonable to suppose that it was for want of this that they had suffered. The substituted plants, that had been put into the case that night, were the ones really analyzed, and used as evidence of the assimilability of free nitrogen. Dr. Pugh, who communicated this information to me, received it directly from one who saw the sickly plants in the case at night, and the healthy ones there the next morning. This piece of shameful history offers the only solution of what would otherwise be an inexplicable riddle.

Furthermore, I believe in these results that have been given us by Boussingault, and by Lawes, Gilbert, and Pugh, because they are reasonable. They are in full accord with what we know of the chemical properties of nitrogen, and of the kind of food, other than nitrogenous, that the plant depends upon for sustenance.

Any who have studied chemistry at all know that there are two sharply distinct classes or substances dealt with in that science, namely, the elementary substances, and the chemical compounds; that the elements are bodies that we have not yet been able to break up into two or more different and distinct bodies; that a compound body is made up by the chemical union of two or more of these elements; that oxygen, nitrogen, gold, silver, iron, etc., are elements; and that water, ammonia, phosphoric acid, lime, etc., are compound bodies. Now the plant is made up entirely of compound substances-and, leaving for the moment its nitrogenous food out of consideration, with respect to all its other food it is absolutely certain that it feeds only on compound bodies or chemical compounds; this is one good reason why we should expect that it would not feed on the element, nitrogen, but on some of the various compounds of nitrogen which we know by experience

to be excellent plant food. Another good reason is that, of all the elements, nitrogen is the one most unwillingly forced into chemical combination; there is not another element of common occurrence that is so well satisfied to remain alone by itself as nitrogen is. Very powerful chemical persuasion has to be brought to bear upon it, to get it out of its state of isolation; never was the most confirmed old bachelor more obstinate in maintaining his bachelorhood. It would be singular, indeed, if the plant, while feeding as to everything else on chemical compounds only, should have the heavy work put upon it of forcing unwilling nitrogen into combination. It is evident enough from all our experience that it does not do that work if it can get nitrogen elsewhere-and there is not a particle of reliable proof that it does that work under any circumstances whatever.

Other chemists in France have investigated this question on a small scale, but with contradictory results. There is not time to speak further of their work. But I must give a brief account of the experiments made by Professor Atwater, of Connecticut, within the past three or four years. These were made with peas, grown in sand which had been completely freed from plant food by washing and strong heating, after which it could contain no nitrogen. The plants were fed with solutions applied to the sand, containing known quantities of all the nutrients required, including a certain amount of nitrogen compounds. They were left in the open air, except when necessary to put them under shelter to prevent them from getting any unknown quantities of nitrogen compounds from rain or dew. In all but one out of fifteen such experiments, carried on in two successive years, there was a gain of nitrogen over and above what was supplied in the seed and food. This gain was in two cases fully equal to all that the plants took from the nutritive solutions with which they were fed, and the plants, according to the observations of the experimenter, seemed the better able to make these gains, the more the conditions of their nourishment, as to the quantity and kind of food supplied, were like those of ordinary growth in the field. On the basis of his results, Prof. Atwater estimated that an acre of peas, fairly well fed, might gather in, from some source other than the food supplied in the soil, from 70 to 120 pounds of nitrogen. It would require over 700 pounds of nitrate of soda, costing about $19, to supply 120 pounds of nitrogen.

The conditions of Prof. Atwater's experiments were such that there would seem to be no source from which this nitrogen could have been derived other than the atmosphere. But still he does not venture to claim for his results that they necessarily give support to the doctrine that free nitrogen is assimilable. We are, then, naturally led to consider the atmosphere as a source of combined nitrogen. There is always a minute quantity of ammonia there, in a gaseous form, and a minute quantity of nitrate. According to the theory of an eminent French agricultural chemist, the millions of pounds of nitrates carried into the sea every year by all the great rivers, which is almost entirely the product of the wastage of the human and other animal inhabitants of the landare converted, through the agency of the vegetable and animal life of the sea, into ammonia. This is given off into the air above the water, and wafted by the winds over the land. Thus, if this not unreasonable theory be true, there is provision for the constant replenishment of the supply of combined nitrogen in the atmosphere.

When we

Although the quantity appears to be small-only one part in 530,000 parts of air-yet in the layer of air, four miles high, over each acre of land there are about 140 pounds of this plant food, very precious to the crops if they can get hold of it. consider that the air is in constant motion, not only in horizontal directions but also upwards and downwards, it is not difficult to understand how a large portion of this ammonia may be brought in contact with vegetation and the soil, during the growing season. But, when it comes within reach, how can vegetation take possession of it?

First. To some extent no one can say how much-through the foliage. It has been proven by experiment that a plant can supply itself with nitrogen in this way, if its leaves are exposed to air containing ammonia gas. It is very natural that clover, with its great abundance of foliage, should be supposed to have the power to help itself to nitrogen compounds from the air more liberally than wheat with its much smaller leaf surface; and this view appears to be supported by the well known fact that clover is a good crop to come before wheat, which needs nitrogen in the soil. But such very few experiments as have been performed, to test this supposed special feeding power of clover on nitrogen compounds in the air, do not support this view; and the beneficial effect of clover preceding wheat can be accounted for, at least to a

large extent, in another way. Those who so strongly insist that clover feeds upon the air forget that in every arable soil, such as clover is usually raised in, there are many hundreds and often some thousands of pounds of nitrogen in chemical combination, although in forms not readily assimilable. But, for all that, it may not be denied that, with the breezes almost constantly bringing fresh portions of air in contact with the foliage, at least a little and perhaps more than a little of their nitrogen may be gained in this way. But it should be noticed in this connection that many of Boussingault's first trials were made under very much the same conditions as those fixed by Prof. Atwater. In nearly all cases there were slight gains of nitrogen when the plants were grown with exposure to free air; but they were very small, falling very far short of those made by Prof. Atwater's plants.

But this ammonia of the air can also reach the plant by way of the roots, through the power possessed by the soil of absorbing gases within its pores. That such absorption of ammonia does take place has been proven by experiment. It is an operation that may go on all the time, day and night alike, and during as much of the year as the soil is open to the access of the air. It cannot be told how much combined nitrogen may be brought within reach of the crops in this way, for it is about impracticable to determine with any degree of accuracy the rate of this absorption. Koenig in Germany estimated it at about thirty pounds per acre and year; but in such a manner that his result was not after all much better than a pretty reliable guess. If the quantity is as large as this, however, it is a valuable contribution to the nitrogen supply.

Perhaps you are acquainted with the history of that rather remarkable system of culture, that was carried on for a dozen years or more by Rev. Mr. Smith, on the Lois Weedon farm in England -the results of which furnish such a striking illustration of what can be accomplished by tillage alone. The fields were divided off into strips three feet wide. In the first year of the course, every alternate one of these strips was planted with three rows of wheat, a foot apart; the spaces thus left between the rows being wide enough to permit full and complete culture by hand, during a large part of the growing season. The unoccupied three-foot strips were most thoroughly cultivated during the whole season; largely by hand labor. In the following year these unoccupied strips were in their turn planted with wheat, in rows a foot apart,

and the planted strips of the previous year were in their turn subjected to thorough tillage. Thus the system was continued for twelve years and without the use of a particle of manure. The results were somewhat astonishing. You will observe that on each acre of wheat only half was really occupied by the crop, in each year; while the other half, consisting of the three-foot vacant spaces, was being cultivated in preparation for the next year. But on each acre so treated-only half of it really bearing a crop, and that half in rows a foot apart-the yield was as great as on manured land prepared for and sown with wheat in the ordinary manner. The average crop per acre was 25 bushels; and in the eleventh year the yield amounted to 37 bushels, with 2 tons of

straw.

Now experience and experiment go to show that wheat is, generally, especially thankful for a manuring containing nitrogen ; on Mr. Lawes' experimental grounds any other constituent of manures could be spared better than the nitrogen; hence it is reasonable to infer that the extremely thorough and unceasing tillage of the soil at Lois Weedon, exposing as it did constantly a fresh and porous surface to the air, so facilitated this direct absorption of ammonia, or (as it may yet appear) of nitrogen in some other shape, from that great reservoir, as to make these large crops possible without the addition of any nitrogenous manure to the soil.

There is yet another way, already incidentally named, for nitrogen compounds in the air to reach the plant through the soil. Besides ammonia, there is always some nitrate in the air. Both compounds are very soluble in water, and consequently every rain will carry nitrogenous plant food to the soil. At several of the experiment stations in Prussia, the quantities of nitrogen thus brought within the reach of vegetation during the year were carefully determined; these quantities were found to be quite different in different places; the largest amount was 21 lbs. to the acre, and the smallest 2 lbs. ; and it was also found that nitrogenous manures were most effective at that place where the natural supply of combined nitrogen was smallest. This is one observation going to show that these natural supplies have an appreciable value.

Various averages have been given for the quantity of combined nitrogen thus carried down to the soil in the course of the year. Where extremes may be so far apart, averages have to be taken