shell, and naturalists determine different species of helix by the presence or absence of this brown color in the lip of the shell. These rings and lip owe their brown color to reduced manganese. The soil gave it to the plants and these to the animal, and the snail is so closely related to this occurrence of manganese in plants, that the species can not exist without it in the plants upon which it feeds; but this manganese certainly plays a more important part in the internal economy of the animal than merely that of ornamenting its shell. If the manganese be necessary for the snail, it would be very strange if we came to the conclusion that it was a matter of indifference to the plant, in its development, from which plant the snail derives its nourishment, and we thus come to the conclusion that this metal is at least an actual and real constituent of the plant in which it is found. Next, many chemists, in the course of the last ten or fifteen years have discovered copper in plants, and others again have discovered this copper in no inconsiderable quantity in the shelless snail, which is so great a pest to agriculturists and horticulturists. The regularity with which copper is found in our most cultivated plants, e. g. wheat, and from which the snail which lives upon them derives it, induces us to suppose the great probability that copper is also a necessary constituent of many plants.

This observation in reference to the occurrence of copper in plants was enigmatical so long as the wide-spread distribution of copper in the soil was unknown. My experiments, heretofore mentioned, have cleared up this difficulty, and they also induce me to seek the metals and other materials found in the soil, regularly, though in minute quantities, in the plants nourished by the soil containing them. To obtain an answer to this question in such a manner that not a doubt would remain, that man, who with his wilfulness and peculiar requirements is always interfering with the quiet developments of nature, had had any influence, I selected for my experiments partly our common forest trees, which grow without the soil having been modified by man, and partly turf, which is formed of the remains of vegetables which also grew without man's interference. I consequently examined beech ashes, which, as is well known, contain large quantities of potash, but in which I now found, as my attention was directed to the metals, lead, copper, and tin, besides the far more abundant and wide-spread metals, iron and manganese. I next examined the ashes of the oak, in whose ashes the metals are far more abundant than in the beech, and found iron, manganese, copper, tin, lead, zinc, cobalt, probably nickel, and besides, barytes. In the ashes of the fir tree I found proportionally more tin, a very small quantity of copper, and still less lead, next barytes, besides iron and manganese. I examined the birch tree

also, and found, besides iron and manganese, tin, copper, lead, and a relatively large quantity of barytes. In turf ashes were found copper and tin, probably nickel, besides iron and manganese. To examine a tree from the tropics I selected the mahogany, which left an ash upon being burned very rich in iron, whose quantity of ashes formed nearly one per cent of the weight of the tree. These ashes contain, of the matters here in question, a relatively large quantity of copper, a small quantity of lead, an important quantity of tin, and a trace of zinc.

From all these examinations one is led to believe that these metals, as well as barytes, are necessary constituents of the plants examined, and a person is induced to believe them as indispensable as phosphoric acid, potash, and lime. That they occur only in such small quantities in plants, and yet perform such an important part in their life and development, may be explained by saying that they are in part poisonous, as copper and lead, and in part are very energetic in their operations, as all the others, including barytes, and only small quantities can thus produce powerful

effects.

If we could present the peculiarities of these matters in the economy of the plant, and point out the difference between these and the before named substances, which play a part in some plants, and group themselves according to the different organs of the plants, as potash in the fruits, phosphoric acid in the seeds, and silicic acid in the fibres, &c., we might perceive that these are joined to particular families of plants, and stand forth as constant constituents of them. We have as yet but little experimental knowledge with regard to the distribution of poisonous and energetically acting materials in the vegetable kingdom, but we are in possession of some observations which point to a law of the kind I have designated. These relations become evident much more readily when we take salt water plants into consideration, than in the more highly developed plants, partly because they contain much larger quantities of inorganic matters, and partly because the conditions under which they are produced are much simpler, as they draw their nutrition almost exclusively from the surrounding salt water. With regard to these plants, and particularly with regard to the proper tang species (kelp ?) it is well known they contain a substance known as iodine, and which is found in such small quantity in sea water that the most delicate analyses alone can detect it, and that we do not use sea water for the production of iodine, in which it originally belongs, but plants which have already collected it. Among the tang species there is one species, the laminaria, used almost exclusively for the production of this rare material. The laminaria are the iodine plants.

Another of our salt water plants which we also call tang, (tong) although it belongs to an entirely different species, is the bendel tang (string seaweed), zostera marina. This plant extracts manganese from sea water in which it occurs in only such minute quantities that the finest analysis alone is able to detect it, but the zostera marina contains it in such quantities that when its ashes are subjected to the action of hydrochloric acid, chlorine is developed freely, just as it is developed when brown stone, the most important manganese ore, is exposed to the action of the same acid. This manganese must exist in the plants in a soluble combination, because when the plant has been exposed to the influence of the sun, wind, and rain, upon our sand beaches, only a minute portion of the manganese is found remaining, and to find it in a large quantity, fresh and perfectly-developed plants must be selected toward the fall of the year. Zostera marina is a manganese plant.

Upon the so-called Galmeiberg-calamine mountain-near Aix-la-Chapelle, there occurs a little violet peculiar to that region. It has been called calamine violet, (viola calaminaria). It contains zinc, and is so characteristic for this ore of zinc, calamine, that it will only grow upon deposits of calamine, and it has been used as a guide in the detection of new deposits of this important zinc ore. When it is planted in gardens it changes its nature and appearance, probably because the soil does not contain a sufficient quantity of zinc to secure its development. This violet is a zinc plant.

Is it not now probable that in time, and by means of continued examinations, we shall find copper, lead, tin, cobalt, nickel, and barytes, plants, nay, that every metal which has not yet been found in the vegetable world, has nevertheless its particular plant, of which it is characteristic. A French chemist in the last century affirmed that he had discovered gold in the vine, and this assertion was entirely neglected, as it was made at a time when chemical analyses were not very exact, and because it did not conform to our then circle of scientific knowledge, but it deserves to be taken up anew, and examined with all the means of assistance which more modern analyses afford.

So much at least is rendered evident by these examinations, that metals have a part to perform in the vegetable world; that a lack or excess of them in the soil must have a decided influence upon the growth and development of plants. If wheat always contains copper, which seems to be evident, from the analytical examinations made, we are justified in the supposition, until the contrary is proved, that a soil which does not contain copper is not suited to the culture of wheat, and it is not improbable

that an increased quantity of copper in the soil will have a decided influence upon this plant's successful growth.

Every one who has cultivated plants has, more or less, felt the danger of the enemies which have beset nearly all our cultivated plants during the last few years, in the form of a multitude of small, low organisms, which produce, or at least evidence diseases in these different plants. We know these diseases as rust or smut in wheat, the potato disease or rot, mildew in the grape, or vine disease, olive tree disease, and some years the currant and gooseberry have been attacked by like plagues. The causes of these diseases are probably of very different natures, but most vegetable physiologists agree that the fungus or fungoid organisms which occur as an external sign of disease, can only obtain their power over the plant when it has already become weakly. As it now appears settled that a small quantity of the above mentioned inorganic substances forms a necessary condition for the well-being and development of plants, the question, whether an entire lack, or a too small quantity of these energetic mineral substances in the soil may not induce the sickliness of plants, which sometimes assumes the character of epidemics among the human race, deserves particular attention.

All agree that this sickliness of plants is in a great degree owing to excessive cultivation, that is to say, to the active interference of man to produce a rich yield of the given plant. But in this expression, "excessive cultivation," there lies a great uncertainty in regard to the changes which grow out of it in the soil and the plants. Over culture-excessive cultivation, may have the effect of making the soil too porous, so that it may become surcharged with organic matters, and be brought into a state of unhealthy fermentation, or by means of the atmospheric air develop too large a quantity of carbonic acid, and an excess of this may act injuriously upon plants, by favoring the abstraction from the soil of too large quantities of inorganic matters, or by favoring the accumulation in the soil of other inorganic elements.

I will now propose as a subject for more exact examination, whether one effect of excessive cultivation may not consist in this, that the ener getic mineral substances which form the subject of the present communication, have been extracted from the earth in a relatively too large quan tity, so that the plants cannot obtain a sufficiency of them for a perfect and vigorous vegetation.

It has been demonstrated by my experiments that the rarer metals in the ashes of plants, taken altogether, stand in a different relation to iron from what they do in the soil, there being, relatively, a much larger proportion of the rarer metals taken up by plants than of iron. This is ap

parent first with manganese, while we are unable, in a large proportion of our different kinds of soil, to demonstrate, except with great difficulty, the existence of manganese, it can be shown in the ashes of plants with the greatest facility, and while generally very peculiar means are required to demonstrate the other metals except iron, in the soil, the existence of copper, lead, tin, &c., in the ashes of plants, can be evidenced by very simple chemical operations. Here, then, a concentration, a collection of these rarer matters has accrued, caused, doubtless by the solubility of their ores in water charged with carbonic acid. Let us consider, now, the peculiar mode in which manganese occurs in sea-weeds: It is in combinations soluble in water, probably with organic acids. As the manganese becomes insoluble in water upon burning the plant and it is not at all unreasonable to suppose a similar condition of the other metals, it follows again that they would be exposed, upon the rotting of the plants, to be washed away, and the soil would thus lose more rapidly these, according to all proba bility, highly necessary constituents of a luxuriant vegetation. A consequence of these relations is that the soil must lose these materials by means of active cultivation, and our manures are not able to replace them in a sufficiently large quantity.

It lies in the nature of the matter that the propositions here laid down must be uncertain as yet. The matter is too new, and our observations have been in this regard too limited to cause us to stop, satisfied with our investigations, but we should strive for a far more extended experience before we consider the matter established and decided; and the object of this communication is especially to direct the attention to these substances, which have not hitherto been considered as plant-nourishing. If only a small part of what I have here expressed, as based upon my own and other chemists' experiments, be confirmed by future experiments and observations, an actual progress in our theoretic sciences of the nourishment of plants will have been made, as well as in our practical knowledge of the means of calling forth a strong vegetation.

I will now close this series of remarks with a definite proposition. It is well known that a much-used, and according to my experience, very useful means of preventing smut in wheat, is to soak the seed in a weak solution of blue vitriol, (sulphate of copper). If the remarks I have before made are not without foundation, then the copper serve to supply the young plants with this productive materials for nourishment, and thereby protects it from the attacks of those lower organisms. My proposition is that the same experiment be made with the potato; that when planting they shall be carefully soaked or moistened with a very weak solution of blue vitriol. It must not be forgotten that copper is a very poisonous