in the plant, he must be assisted by the physiologist, who teaches him the form of the substances examined, the form of the organs constituting those substances, the position of substances in the plant, and finally, the general function of each organ. For physiology is the science whose object is to ascertain in this branch of it (1), the origin of the plant-organs (2), their functions in the life of the plant, and (3), the relation of these organs to the external powers of nature; its province is to consider closely, also, the specific qualities of each plant. Chemistry can not do this to the same extent; for the specific qualities appear rather in the external and internal form than in the chemical composition, and the crop depends in many cases entirely upon the specific qualities of a plant-species. The length of roots, their covering, the heighth of stem, the growth of the whole plant -all these points are important as to good crops. But here the chemist can be of no service, for, simple as the structure of the plant appears, it is nevertheless difficult for chemistry to consider it in its relation to the life of the plant; for this is physiology. If the chemist examines a plant, he is obliged to cut, pound and bruise it; the substances found by him in the plant are sometimes already in a solved condition, sometimes insolved; but the chemist can not ascertain that. A glance into the microscope, however, affords the practiced eye perfect security in a few minutes. Substances appearing in very small quantity and in a transitory manner will probably not attract the attention of the chemist, while a microscopic investigation proves that the position and manner in which the substances are contained in the plant assign to it an unexpected importance.

IV. Has physiology of plants been developed so far as to be of material service as a practical science? We answer, emphatically, in the affirmative. There is, it is true, as yet no work on physiology of plants that brings the physiological questions in direct connection with the requirements of agriculture. But whoever knows the standing of the present physiology of plants will admit that the methods of observation are not less exact than those of chemistry; that there is a general knowledge of the external and internal structure of plants, which would lead to many practical conclusions and applications, if they were applied in this particular sense.

The physiology of plants does not appear, in its present condition, to have much bearing on practical life, its object having heretofore been to find general laws of plant-life; isolated facts were of a value only in such a degree as they aided in establishing general laws. What could have induced botanists to care for a practical realization of their studies, since practice, indifferently understanding its own advantages, did not solicit the assistance of the science of plants? In looking over the works of agricul

tural botany, one is forcibly struck by the circumstance that they are at least some twenty years behind the status acquired by physiology. If we consider what physiology of plants has done in twenty years, or during that very epoch in which chemistry began to rank itself among the agricultural sciences, we must award to it a capacity of development and a strictness of observation, which is granted only to purely physical doctrines. And if we ask who did all this, we meet with names of such men only as were not occupied in practical agriculture or horticulture. It was the pure desire for knowledge on the part of a few men, living mostly in wretched poverty, that has developed the science of physiology of plants; there were a few that only resolved to promote this science, since neither public nor private positions, or salaries, could induce others to engage in this work. But the nature of science claims acknowledgment of merit, or else talent will be paralyzed; and it is especially the series of natural sciences which require money and material wherewith to promote them. While everything else in the whole world may be purchased, the most precious thing-knowledge-is claimed as a gratuity. One thing must not be overlooked: practice requires definitively circumscribed principles, and no such general laws of plant life as the botanist theoretically endeavors to establish; it needs, rather, positive answers to positive questions, which are ultimately nothing else than questions of money. In order to answer such questions, a general theoretical knowledge is the first condition; for this reason professional physiologists only will be competent for the task. But another and essential condition is this: the physiologists must be enabled to cultivate their science in all its minutiæ, so as to adapt it for actual practice. The demands of the latter, differ materially from those of science. Science demands truth, and the most general truths; practice is in quest of gain, and truth is to assist it to obtain this gain; practice expects and demands gain from relations altogether special, from a positive capital; it must, therefore, grant to science the means for investigating these relations. It matters very little to the theoretical physiologist whether this or that species of wheat contains per cent. of gum; but this becomes a vital question to the practical physiologist. He will devote the greatest attention to a phenomenon that seems to be very inferior to the theoretical physiologist.

V. He who does not devote attention to science proper, imagines that the answering of scientific questions is a very simple matter. First, because everything is, in nature, connected with everything else, and especially as the very slightest circumstances are often, in practice, of great importance, it is impossible for uninitiated men to conceive an idea of the difficulties so often connected with answering questions. If, therefore,

physiology is to serve agriculture, the means must be procured for the physiologist to engage himself exclusively with practical questions; suffi cient time must be allowed to him to investigate such questions with scientific accuracy, and to accustom himself to the methods of practice, in the same manner as means and time have been afforded to the chemist to devote himself wholly to his practice.

VI. The object of an agricultural physiologist is to aim at that which coincides with that of the agricultural chemist. Both are to find the means of obtaining a profitable crop under given circumstances, and of aiding the circumstances offered by nature, in order to prevent the crops from becoming a prey to accident, temperature and soil. But each one of these must do this in his own way: the chemist, according to the principles of chemistry, while the physiologist must bring the physical effects in that connection with the process of formation and the structure of cultivated plants, which may lead to answer practical questions.

VII. It may be asked, why practice has as yet furnished so few available experiences, and how it happens that after a repetition of the same experiments during thousands of years-for every seeding is an experimentthe practical men have made such limited penetration into the inner working of plant-life? The chemist will answer: Because the scale has never been used, and because the crops have not been specified and weighed, nor the kinds of soil been analyzed, etc. That is perfectly correct, as far as it goes; but pomologists do neither weigh their crops nor analyze their manure, and, nevertheless, pomology is based on a system of theoretical principles almost annihilating the effects of accidents. The pomologist has not only quality but also quantity of crops so much in his power, that if he perceives a tree bearing little and poor fruit, he does not attribute it to weather, or soil, or accident, but to the gardener having charge of the tree. In fact, scientific pomology is sufficiently far advanced to obtain the results desired, under almost all circumstances. A similar great improvement may be found in other parts of gardening, which, strictly speaking, is to be considered as simply practical physiology of plants. Why could not thus much be attained in agriculture? But this requires the capacity of close observation of good combination; which (capacity) can only be acquired by the naturalist, and with much labor. In order to conceive a crop as the result of temperature, soil and sowing; in short, in order to find out the causes of crop, it does not suffice to till a field so and so many years, and to observe all the statements of the forefathers; it requires a naturalist, i. e., a practiced observer; and not everybody has the capacity for this work. If old practitioners, in opposition to science, appeal to their experience, let them prove, in the first place, their capacity for observa

tion; for the value of experience does not consist in the number of observed cases, but in the capability of finding from them the causes and connections; and this is only obtained by talent, in connection with multifarious preparatory studies. Taken all together, this statement will show that practice certainly may find and adopt rules, but that it has not yet and could not have brought about a science of agriculture. If the practitioner happens to be a talented observer, he may, indeed, derive new principles from his experiences, but he will follow them instinctively, without being able to impart to them the character of scientific and generally valid principles; just as Liebeg demonstrates that many well educated agriculturists do not understand the action of manures. Liebig says:

No one will maintain that it is a matter of indifference to the husbandman whether the ideas or principles which guide him in his operations are true or false. The success of his practice is evidently based on two things-that he knows what he is doing, and that he does the right thing in the right way; so that, as every scientific view in agricultural matters becomes in its application a money question, it may be of interest to him to learn the exact state of our knowledge respecting the principles and theory of manuring.

Science has taught us that plants require for their normal growth a number of elements (carbon, phosphorus, silica, ammonia, potash, lime, magnesia, &c.), most of which are furnished by the soil; and it has been established by the direct experiments of Stohman and Knak, that these varions nutritive substances possess an equal nutritive value-that is to say, that all must exist together and work together in the building up of the vegetable fabric in its normal condition. Taking the case of those plants which supply food for man or beast, it is found that in the process of their nutrition, none of these different substances can replace or discharge the functions of another; so that, if one be wanting, although there may be an abundance of the rest in the soil, the plant cannot grow; if one of them be insufficiently represented in the soil, the harvest will suffer in a certain proportion to the element that is wanting; ammonia, therefore, possessing no higher nourishing or manure-value than lime, phosphoric acid no higher value than potash, &c. This doctrine, based on natural laws, is not generally admitted by English farmers, and has even been stated to be inapplicable to English soils. Starting from the result of a number of experiments made on a small piece of ground, a manufacturer of manure in London maintains, that there are degrees in the value of each of the nutritious elements, in a manure which could be easily determined, as estimated by the amount of crops produced on any field after being manured with it.

If the produce were increased by one element and not by another, he concluded that the first possessed a preponderating value over the second. In his trial fields, for instance, phosphoric acid had little or no effect in increasing the corn crop; whilst on the other hand, by manuring, with the same phosphates, a turnip field, a much larger crop of roots was produced than on a field unmanured. In manuring with salts of ammonia, the result was reversed; the corn crop being increased by them, but no perceptible effect being produced on turnips.

A so-called practical doctrine was derived from these facts; they proved, it was said, that nitrogen (ammonia, nitric acid,) was an especially efficacious ingredient in manure for corn, and phosphoric acid equally so for turnips.

The specific efficacy of ammoniacal salts on corn was further shown by the fact, that a field manured for several years with them alone produced equally large crops of corn during that time; and likewise, in a very striking manner, ceased on the third year to yield a crop of turnips. The great efficicacy of super-phosphate of lime on turnips was shown by the other

fact, that a field which, unmanured, gave no more turnips on the third year, produced nine crops, one after another, when this manure only was applied.

Now, a very slight reflection is sufficient, I think, to show us that this mode of testing the efficacy of the several nutritious elements of plants, is idle and useless; for if it be once proved as an empirical law, that ammonia, phosphoric acid, potash, lime, &c., are nutritious elements, and as such indispensable for all plants, there can be no further doubt of their efficacy in any single case, and no additional proof of their utility, or value, will therefore be needed. If by manuring a cornfield with salts of ammonia, or a turnip field with super-phos phate, the crop of corn or turnip roots be increased, the fact is not in the least wanted to prove the efficacy of those manures, which is already known and undisputed; nor if by manuring a field with potash or lime, &c., no increase of crop be observed, does it therefore follow that these substances are not in themselves efficacious.

It is easy to understand that phosphoric acid, or ammonia, may not, either alone or together, exert the slightest influence on the growth of a plant. Supposing phosphoric acid, potash, lime, magnesia, silicic acid, &c., to be indispensible conditions for the efficacy of ammonia, and supposing ammonia, potash, lime and silicic acid to be indispensible conditions for the efficacy of phosphoric acid, it follows that if a wheat field, manured with ammonia alone, gives a higher return than it does without it;, all that is proved is, that this field contained an excess of phosphoric acid, potash, lime, &c., inefficacious because a certain proportion of ammonia was wanting, but rendered efficacious by increasing the quantity of ammonia in the soil; while without this excess of available but not efficacious element, the largest manuring with ammonia would have had no effect. In like manner, it is perfectly plain, that if a field be deficient in potash, of which turnip roots want ten times as much as they do of phosphates, supposing the available quantity of potash be only sufficient for the formation of three crops, then only three would have been attained, and the largest dressing with super-phosphate could not produce nine.

Experiments of this kind indicate only what elements of food are abundant, or wanting, in the soil, and it is impossible to prove by them anything about the efficacy of a manure element. The increase, or non-increase, establishes only the quality or nature of a field, the knowledge of which is, undoubtedly, very useful to the owner of the land, but to him alone; for it is of no avail to his next neighbor, if the quality of this neighbor's land happens to be different. Numberless experiments of the same character have been repeatedly made in Germany, at the instance of several agricultural societies. On many cornfields, manuring with ammonia salts had not the slightest effect, while super-phosphate of lime alone produced much larger corn crops than any other manure had afforded. It is really astonishing that farmers, who call themselves' men of experience, can be made to believe that because a manure bas produced, on a field in a certain country, a high return of corn or roots, it should produce an equal effect, and possess an equal value, on all the fields in Great Britain; for, if the efficacy of a manure, A, be believed to depend on the presence and quantity of the manure B, C, D, &c., it must be assumed that all the fields in a country, or land, contain the same quantity of B, C, D, &c. Now, it is an indisputable fact, that there are scarcely two fields of the same country, often not two fields on the same farm, which possess the same identical, geological, chemical, or mechanical character; so that the quantity of the manures, B, C, D, &c., varies in each instance. It must be plain, therefore, that the same quantity of manure, A, be it ammonia, phosphoric acid, or potash, must necessarily have quite a different operation in proportion as the fields are differently constituted. Even stable dung, which contains all the nutritive elements in conjunction, produced different effects when applied in the same quantity to different fields.

With reference to practical farming, it is important to remark, that it follows as a corollary from the law of equality of nutritive value belonging to the constituents of food, that the element, or elements, which are either wanting in the soil, or are contained in it in insufficient quantity, are the ones which will prove of preponderating value in the manures applied.