most part, presented in journals or other publications which are quite out of the reach of the general student. These results, together with the remarkable studies of English experimenters, comprise nearly all which is positively known with reference to the life and growth of agricultural plants. This widely scattered mass of facts embraces, however, just what every progressive farmer wants to know; while not one in a million has the time, the means and the ability to obtain, translate, digest and arrange them for himself. It is in the highest degree creditable that one of our Professors should undertake and satisfactorily accomplish the formidable task of bringing order out of such a chaos.

In the above named volumes Prof. Johnson has presented in a convenient form, the established facts of Physiological Botany, so far as they relate to the cultivation of crops, and he has stated in clear language the cardinal principles upon which successful agriculture must depend. The following is from the Preface to How CROPS GROW:

"For the last twelve years it has been the duty of the writer to pronounce a course of lectures annually upon Agricultural Chemistry and Physiology to a class in the Scientific School of Yale College. This volume is a result of studies undertaken in preparing these lectures. It is intended to be one of a series that shall cover the whole subject of the applications of Chemical and Physiological Science to Agriculture, and is offered to the public in the hope that it will supply a deficiency that has long existed in English literature.

"The progress of these branches of science during recent years has been very great. Thanks to the activity of numerous English, French, and especially German investigators, Agricultural Chemistry has ceased to be the monopoly of speculative minds, and is well based on a foundation of hard work in the study of facts and first principles. Vegetable Physiology has likewise made remarkable advances, has disencumbered itself of many useless accumulations, and has achieved much that is of direct bearing on the art of cultivation.

"The author has endeavored in this work to lay out a groundwork of facts sufficiently complete to reflect a true and well-proportioned image of the nature and needs of the plant, and to serve the student of agriculture for thoroughly preparing himself to comprehend the whole subject of vegetable nutrition, and to estimate accurately how and to what extent the crop depends upon the atmosphere on the one hand, and the soil on the other, for the elements of its growth.

"It has been sought to present the subject inductively, to collate and compare, as far as possible, all the facts, and so to describe and discuss the methods of investigation that the conclusions given shall not rest on any individual authority, but that the stu

dent may be able to judge himself of their validity and importance. In many cases fulness of detail has been employed, from a conviction that an acquaintance with the sources of information, and with the processes by which a problem is attacked and truth arrived at, is a necessary part of the education of those who are hereafter to be of service in the advancement of agriculture. The Agricultural Schools that are coming into operation should do more than instruct in the general results of Agricultural Science. They should teach the subject so thoroughly that the learner may comprehend at once the deficiencies and the possibilities of our knowledge. Thus we may hope that a company of capable investigators may be raised up, from whose efforts the science and the art may receive new and continual impulses.

"In preparing the ensuing pages the writer has kept his eye steadily fixed upon the practical aspects of the subject. A multitude of interesting details have been omitted for the sake of comprising within a reasonable space that information which may most immediately serve the agriculturist. It must not, however, be forgotten, that a valuable principle is often arrived at from the study of facts, which, considered singly, have no visible connection with a practical result. Statements are made which may appear far more curious than useful, and that have, at present, a simply speculative interest, no mode being apparent by which the farmer can increase his crops or diminish his labors by help of his acquaintance with them. Such facts are not, however, for this reason to be ignored or refused a place in our treatise, nor do they render our book less practical or less valuable. It is just such curious and seemingly useless facts that are often the seeds of vast advances in industry and arts.

"For those who have not enjoyed the advantages of the schools, the author has sought to unfold his subjects by such regular and simple steps, that any one may easily master them. It has also been attempted to adapt the work in form and contents to the wants of the class-room by a strictly systematic arrangement of topics, and by division of the matter into convenient paragraphs.

"To aid the student who has access to a chemical laboratory and desires to make himself practically familiar with the elements and compounds that exist in plants, a number of simple experiments are described somewhat in detail. The repetition of these will be found extremely useful by giving the learner an opportunity of sharpening his perceptive powers, as well as of deepening the impressions of study.

The author has endeavored to make this volume complete in itself, and for that purpose has introduced a short section on the The Food of the Plant. In the succeeding volume, which is nearly ready for the printer, to be entitled 'How Crops Feed,' this subject will be amplified in all its details, and the atmosphere and the soil will be fully discussed in their manifold Relations to the Plant. A third volume, it is hoped, will be prepared at an early day upon Cultivation; or, the Improvement of the Soil and the Crop by Tillage and Manures. Lastly, if time and strength do not fail, a fourth work on Stock Feeding and Dairy Produce, considered

from the point of view of chemical and physiological science may finish the series."

How successful Prof. Johnson was in his endeavors, as above set forth, is shown by the reception which his books have met, both in this country and in Europe; having been republished in England under the joint editorship of Profs. Church and Dyer of the Agricultural College at Cirencester, and in Germany, a translation, instigated by Baron Liebig, has been published.

It is safe to say that these volumes may be accepted as an authoritative exposition of the scientific agriculture of the present day, in those branches of which they treat. It is equally safe to say, that they are books not well adapted for light reading. They deserve to be carefully studied, as well as read, and will be of little use unless they are. Two duodecimo volumes, of rather less than 400 pages each, containing all the facts 'gathered during a series of years by scores of laborious investigators, together with the interpretation of these facts, or, in other phrase, their testimony regarding agricultural practice, could not fail to be full to the brim of concentrated mental food. Their contents, amplified with swelling words, extended with a customary amount of blunders, and diluted with twaddle to the consistence of the thin broths supplied to the press by some agricultural writers, would furnish materials enough for a library of great magnitude. As the case stands, either can be had for two dollars, or both for four, and a world of house room saved, with a corresponding economy of time.

It is well to have some such books. The digestive powers of intelligent farmers are not so weak that they need, either physically or mentally, to be fed solely upon slops, or even on milk; and the farmer who has taken a slice of solid intellectual food such as these furnish, has a cud for profitable rumination while his hands are busy with daily routine work. In one respect these volumes are open to less favorable criticism. Those who buy them will do so for the sake of availing themselves of the author's share in the work, and not because of less attractions contributed by the publisher; the paper, binding and general mechanical execution being suggestive of a poverty in marked contrast with the solid wealth within.

To serve the double purpose of more fully, introducing Prof. Johnson to the farmers of Maine, and to furnish valuable informa

*Sold by booksellers generally, or sent postpaid on receipt of price by the publishers, Orange Judd & Co., 245 Broadway, New York.

tion regarding a subject of great practical importance, I am happy in being able, through the courtesy of Secretary Gold, to present here two lectures delivered before the Connecticut Board of Agriculture at their last session.

SOIL EXHAUSTION AND ROTATION OF CROPS.

BY PROF. S. W. JOHNSON.

Mr. Chairman and Gentlemen: Sometime since, I received from Mr. Gold, a letter asking me to address the Board of Agriculture and the gentlemen assembled on this occasion, on Exhaustion of Soils and Rotation of Crops. In that letter Mr. Gold says:

"We want to go further than the common theory of rotation leads us, and to inquire why some crops may be grown for several years in succession, as onions and buckwheat, why corn does not succeed after turnips, why does land become clover-sick.

"Why does the culture of certain crops tend to make the farm richer, while other crops only make it poorer, and in both cases, the gross amount of minerals and ammonia contained in the crops may be the same, or even greater in the enriching crops?

"Are there certain periods of plant growth which may be called the enriching period, and others, as the fruit season, the exhausting?

"Is not wheat, the prince of cereals, the greatest exhauster of the soil for the product taken from a given area?

"Tobacco should not be a very exhausting crop; yet from the fact, that for the particular purpose for which we cultivate it, a very luxuriant growth is required, do we not need to furnish more. plant food than can be assimilated, much of which is lost in the air, and washes away?

"The physical condition of the soil as it is left by different crops is worthy of notice.

"Wheat grows well after peas and clover, also after tobacco; but is not this last owing to the manure left over by the tobacco and the good preparatory culture?

"Corn does not do well after buckwheat, but potatoes do well. "Perhaps my facts may not be facts, but they are believed by a great many farmers, and we want the whole subject overhauled and explained."

After getting here on the ground, and looking over the material

which ought to be considered in connection with these questions, Mr. Gold has promised me that I shall have another hour to-morrow, and I will occupy this morning with a part of the subject.

I cannot promise, however, to answer all the questions which Mr. Gold has proposed. Our knowledge is not sufficient for that. Mr. Gold's admission that some of his "facts may not be facts," shows that investigation is needed to establish fully what is, and to distinguish that from what appears to be, before we can reasonably expect to give explanations. But the very investigations which shall serve in any given case to identify the fact will also assist in understanding the reason of it, and in seeing clearly its bearings upon the other facts which we properly regard as settled. I shall endeavor then, as far as the time admits, .to put before you some of those considerations which seem adapted to furnish guiding ideas in respect to my subject.

By Exhaustion of Soil is properly understood, not a complete deprivation of producing power, but simply a reduction of this power below a profitable point. This is indeed a somewhat indefinite definition, because the point of profit is not easy to decide upon, but it is sufficient for our purpose.

What does exhaustion consist in? It consists either in the removal of certain materials from the soil, materials which serve to feed the crop and become a part of it, and which, by continually taking off harvest after harvest, become diminished in quantity, so that after a certain time there is not enough left in the soil to produce a fair crop, or else it means that the materials which may still exist in the soil no longer occur in that condition in which the crop can make use of them. We may have a soil containing potash in large quantities, many hundred pounds, or tons even, in an acre, taken to the depth of two or three feet; but if this potash exist there exclusively as an ingredient of some mineral which is acted upon so slowly by the natural process of solution that there is no available potash, as we say, nothing which the crop can get hold of, such a soil would be unproductive. Again, we may have a soil which contains but a thousandth part as much potash, but which is fertile from the simple fact that the alkali occurs there in such a state as to become available as rapidly as the crop requires it.

To cure exhaustion, we must either restore the nutritive matters which have been removed from the soil, or we must change the