ducted. We know that drain tubes and aqueducts are often choked by a mass of rootlets which have grown from one little fiber that made its way into them through a narrow crevice, but why should the roots of trees and land plants thus develop in such water unless they find their food in it? In Stoeckhardt's experiments loc. cit., it was observed that rye and oats only developed in a normal manner in saline solutions, when these were diluted from six to ten thousand times! and young clover plants grew luxuriantly, putting forth new roots, leaves and blossoms in profusion, when transferred from the soil to pure water supplied with carbonic acid, to which was added th of clover ashes that had been neutralized with nitric acid.

It is true that most river and spring waters yield by analysis but the minutest traces of potash, ammonia and phosphoric acid, but we cannot perhaps infer with safety that they are actually so deficient in these ingredients, for it may easily happen, as all chemists know, that in the evaporation of a large mass of water traces of salts are likewise carried off,* and in the ignition of saline residues, as is customary in the analysis of a water, much more loss of potash may occur from the ready volatility of chlorid of potassium.

But admitting that our analyses are sufficiently accurate to base calculations upon, and that the soil-water never contains more potash for example than river and well waters; viz., from 2 to 10 parts in 1,000,000,† it must be remembered that the plant is by no means compelled to limit itself for its supplies of mineral matter to that portion of water which it transpires.

The root-cells of a plant placed in a saline solution at once establish osmotic currents, in virtue of the mutual but unbalanced attractions that exist between the cell-walls, the liquid of the cell, the surrounding liquid and the saline and organic matters in solution in these liquids. The assimilating processes going on in the cells are constantly transporting matters forward into the newer growths; or else removing them from solution in the sap, and causing their deposition in the solid form. These are the prime disturbances that operate the currents, and to restore the matters thus removed from the liquids of the rootcells, external matters held in solution diffuse inwardly. If a plant has a large leaf surface exposed to the free air, from which water rapidly evaporates, water diffuses into the root-cells if it be

* In Liebig's Chemistry applied to Agriculture and Physiology (5th German ed., p. 102, et seq..) may be found an account of some of the more striking instances of this volatilization. My friend, Dr. Robert A. Fisher permits me to mention the result of some of his researches that bear on this point. He found in fact that a quantity (very small indeed but still sufficient to be estimated by volumetry) of caustic potash is carried off in the vapor when its aqueous solution is distilled.

Eichhorn found in 1,000,000 parts of distilled water that had been in contact with a soil for ten days, 57 parts of potash.

SECOND SERIES, VOL. XXVIII, No. 82.-JULY, 1859.

present in the soil, and thus the normal humidity of the structure is preserved. But if the plant be situated in a close hothouse, or in a Ward's case, the atmosphere of which is constantly saturated with aqueous vapor, there can be no evaporation of water from the leaves, there can be no transpiration of water through the plant and no absorption of it by the roots, except to supply what becomes a solid constituent of the tissues or is decomposed in the nutritive process. The same is true of potash or any other substance held in solution in the soil-water. As a result of this principle the land plant collects the potash, phosphoric acid, silica, &c., needed for its organization, from the vastly dilute solutions of these bodies which form the water of wells or of the soil, just as the fucus gathers its iodine from the ocean, although the marvellously delicate reagents which we possess for iodine scarcely enable us to detect this substance even in highly concentrated sea-water.

Says Gmelin, (Handbook of Chemistry, Cavendish Soc's. ed., vol. ii, p. 248,) "the quantity of iodine contained in sea-water is so small that Tennant, Davy, Gaultier, Fyfe and Sarphati were not able to find it. Balard, however, found it in the water of the Mediterranean and Pfaff in that of the Baltic, which is nevertheless very poor in iodine." Otto (Lehrbuch 3d ed., 1st Part, p. 452,) observes "while bromine is easily found if not in the sea-water itself, yet in the mother-liquors obtained by its evaporation, and is prepared from them in large quantities, it is still doubtful if iodine can be detected in them.' Again in a note "It is worthy of remark that in preparing bromine from the mother-liquors of sea-water, iodine, so far as I know, has never made its appearance."

Iodine can be detected in a solution of which it forms but 30th part-Otto.

The selecting power which is possessed by plants is fully explained and defined by osmotic diffusion. Within certain easy limits the plant imbibes only those kinds of matter and those quantities, which it requires to develop its organism, and which diffuse into it in consequence of assimilation in the cells. These limits are not so narrow or inflexible as to make the finding of the conditions of growth impossible, and within them, the plant lives and expands, but is itself influenced in its life and in the direction of its enlargement, by the quantities, absolute and relative, of the nutritive or soluble matters, that happen to surround it. Could we grow two plants in precisely identical conditions, we should find their composition alike in all their parts. The variations in the composition and amount of the ash of plants is probably connected with the different relative development of the separate organs, and this again (in part) with the relative quantities of food present in the soil water. Thus the ash of

the plant is to a certain extent independent of the soil, but again to a certain extent is affected by it. The absorption of poisons by plants is entirely abnormal and does not affect our statement. Not only does the grand law of osmose (endosmose and exosmose) feed the plant out of such attenuated solutions, but, in all probability it aids the formation of these solutions. Graham has shown in the case of alum and bisulphate of potash that the unequal diffusive tendency of the members of a double salt is powerful enough to decompose it, and he observed that solutions even of the neutral sulphates of potash and soda diffused their basic ingredients into lime-water, more rapidly than the acid; these stable salts thus undergoing partial decomposition.

The investigations of Henneberg and Stohmann already cited, have proved that the absorbent power of a soil is not a purely chemical process, in the ordinary restricted sense; but is in part a physical phenomenon, i. e., it does not depend exclusively upon the presence in the soil, of a certain amount of some peculiar kind of matter, but is also related to the condition and to the relative amount of acting surface of the various materials which react.

Henneberg and Stohmann found that the time of contact between a solution of an ammonia-salt and a soil did not affect the amount of absorption, as much ammonia being taken up in four hours as in a week. This fact indicates that the absorbing substance is in an extreme state of division, to which the pulverized chabazite of Eichhorn's experiments can bear no comparison.

They found too, that a given soil absorbed out of an equal volume of liquid very nearly the same amount of ammonia from equivalent quantities of all its salts, the phosphate excepted.

They observed however that the relative quantities of soil, water and the saline substance, affected the results; thus from a stronger solution a greater absolute amount of ammonia was absorbed, while from a weaker solution a relatively greater quantity was taken up: and further, relatively more was absorbed by a given amount of soil, from a solution of given strength when the volume of the latter was increased.

Finally they found, as has been already remarked, that by diluting with pure water the solution from which a soil had saturated itself with ammonia, a portion of this body is redissolved.

Thus it appears that the very surface-attractions which determine the solution of solid bodies, and occasion osmotic diffusion, also operate in the soil to influence the chemical affinities which are the prime cause of its absorptive properties. The chemical affinity of silicate of alumina for the bases, (probably too that of oxyd of iron and alumina for some of the acids) is modified by the mass of the reacting substances and by that of their solvent; or in other words the cohesive force of the atoms of the com

pound silicates, or the adhesive force of water, (solvent action) for the saline bodies, may neutralize or limit the chemical affinity which determines one compound and give origin to another. Hence the chemical substitutions in the soil, and in the case of chabazite: hence too the perpetual presence of all the mineral food of plants in the water of the soil.

We would not by any means deny the direct action of the rootlets of plants upon the soil, an action which though exceedingly obscure and as Prof. Liebig remarks in enunciating his new views "very difficult to form a conception of," we may admit in some cases.

Liebig in his letters on modern agriculture, p. 43, gives this instance: "We frequently find in meadows smooth lime-stones with their surfaces covered with a network of small furrows. When these stones are newly taken out of the ground, we find that each furrow corresponds to a rootlet, which appears as if it had eaten its way into the stone." We may admit in this case that the rootlets have acted upon the stone, but are not therefore necessarily compelled to assume that the dissolved matters have entered the plant or were dissolved as food, for in such limesoils the excess rather than the deficiency of carbonate of lime is oftener a hindrance to vegetation. In the case of the Lycopodiacea, which contain alumina in large quantity combined with tartaric acid, (Berzelius) or malic acid (Ritthausen) we are, if any where, obliged to look to the plant itself, to account for the entrance into it of a substance absent from all cultivated plants if our numerous analyses are to be credited, and one which is rarely found in river waters, and then in quantity so small as to excite the suspicion that it has been introduced in the reagents, or came from suspended matters.

But it is evident from the facts that have been adduced that it is unnecessary to have recourse to any new theory to explain the access of the soil-ingredients into the plant. In fact it would appear that the view we have felt forced to sustain is the only one admissible in the present state of knowledge-the only one conformable to what we deem well established physical laws.

Conclusion. The function of the soil.-While the researches of Eichhorn are of the utmost value in aid of the theory of the absorption of fertilizing matters by the soil, they do not suffice to give a full explanation of this process. Doubtless all the reactions that occur between hydrous silicates, sesquioxyds and saline solutions may take place in the soil; but in addition to these a number of other changes must go on there, as the soil is so complex and variable a mixture. The organic matters (the bodies of the humic acid group), which are often though not always present in no inconsiderable quantity in the water extract of fertile soils, can hardly fail to exert an influence to modify the action of the silicates. I have found that a peat (swamp

muck) from the neighborhood of New Haven, (containing when fully dry 68 per cent of organic matter) which is highly prized as a means of improving the porous hungry soils in this vicinity, and which when drained grows excellent crops, is capable of absorbing 1.3 per cent of ammonia, while ordinary soil absorbs but 0.5 to 1 per cent.

The great beneficent law regulating these absorptions appears to admit of the following expression: those bodies which are most rare and precious to the growing plant are by the soil converted into, and retained in, a condition not of absolute, but of relative insolubility, and are kept available to the plant by the continual circulation in the soil of the more abundant saline matters.

The soil (speaking in the widest sense) is then not only the ultimate exhaustless source of mineral (fixed) food, to vegetation, but it is the storehouse and conservatory of this food, protecting its own resources from waste and from too rapid use, and converting the highly soluble matters of animal exuviæ as well as of artificial refuse (manures) into permanent supplies. Yale Analytical Laboratory, May 15th, 1859.

ART. X.-On Fossil Plants collected by Dr. John Evans at Vancouver Island and at Bellingham Bay, Washington Territory.—In a letter from L. LESQUEREUX to J. D. DANA, dated Columbus, Ohio, May 12, 1859.

Dear Sir,-Supposing that Prof. Heer who is now engaged in publishing a magnificent Fossil Flora of the Tertiary of Europe, would be much interested in the examination of the plants of Dr. John Evans' survey, of which a short description is published in the last number of your Journal, I sent him a sketch of the drawings prepared for Dr. Evans' report. I have just received an answer to the communication, and as it fixes the value of my species and gives some opinions which are of great interest to American geology, I take the liberty of translating a part of his letter and sending it to you for publication.

Prof. Heer says: "I have hailed with the greatest delight the news which you give me in your letter of 21st March. They are the first rays of light penetrating the dark night which until now has covered the tertiary flora of America, and the day is close at hand, when the fog which still darkens the wonderful flora of those times will be uplifted, and the New World open to us its treasures. They will prove of the greatest interest for the natural philosophy of the earth, and give us most important information as to the relation of climate at the tertiary epoch, and to the secular progression or distribution of temperature over the whole earth. But it is also of the greatest importance for the