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azote, oxide of ammonium, plants incessantly consume oxide of ammonium, azote, water, carbonic acid. What one class of beings gives to the air, the other takes back from it. .... Thus plants and animals come from the air, and thus to it they return; they are real dependents on the atmosphere.
“Plants, then, incessantly take from the air what is given to it by animals, that is to say, carbon, hydrogen, and azote, or rather carbonic acid, water, and ammonia.
“It now remains to be stated how, in their turn, animals acquire those elements which they restore to the atmosphere ; and we cannot see without admiration the sublime simplicity of all these laws of nature, that animals always borrow these elements from plants themselves.
“ We have indeed ascertained, from the most satisfactory results, that animals do not create true organic matters, but that they destroy them; that plants, on the contrary, habitually create these matters, and that they destroy but few of them, and this, in order to effectuate particular and determinate conditions. Thus it is in the vegetable kingdom, that the great laboratory of organic life is placed; there it is, that the vegetable and animal matters are formed, and there they are produced at the expense of the air. From vegetables these matters pass, ready formed, into the herbivorous animals, which destroy a portion of them, and accumulate the remainder in their tissues ; from herbivorous animals they pass, ready formed, into the carnivorous animals, who destroy or retain some of them according to their wants ; lastly, during the life of these animals, or after their death, these organic matters, as they are destroyed, return to the atmosphere whence they proceeded.
“ Thus closes this mysterious circle of organic life at the surface of the globe. The air contains or engenders oxidized products, as carbonic acid, water, nitric acid, oxide of ammoni
Plants, constituting a true reducing apparatus, possess themselves of their radicals, carbon, hydrogen, azote, ammonium. With these radicals, they form all the organic or organizable matters which they yield to animals. These in their turn, forming a true apparatus for combustion, reproduce carbonic acid, water, oxide of ammonium, and nitric acid, which return to the air to produce anew, and through endless ages, the same phenomena.
The discovery of Liebig, of the supply of ammonia or nitrogen to plants from rain-water and snow, will probably be carried to a much further extent, and involve points of great value to agriculture. Already has it been found in Germany, that several seeds of Alpine plants, particularly of some Gentians,
whose germination has hitherto been attended with much difficulty, will grow readily if sown in contact with snow. Now ammonia does not easily evaporate from water at the temperature of snow ; hence these seeds, shed on the surface of the earth, naturally remain a long time in contact with a substance (snow) containing a small quantity of ammonia ; and, indeed, it is not impossible that some of the integuments of seeds, of which, except as a covering, the use is not at present very apparent, may be constructed with a view of serving for absorption, or for some other action in relation to substances requisite for their germination. Many unsuccessful attempts bave been made here to raise plants of Gentiana crinita, of Gerardia, and of Eucroma, from seed gathered in the autumn and sown in the spring ; the probable cause of the failure, according to the above statement, should be the want of the condition, under which it is sown naturally, that is, contact with snow. The seed of Gerardia has a beautiful and peculiar cellular integument.
It is, in fact, impossible at present to divine what may be the results of the attention to these subjects, to which this work has given rise ; that they will be generally beneficial admits of no doubt. It is pleasant to reflect on the general feeling of common brotherhood and citizenship, which such beneficial discoveries engender amongst individuals of various nations. How different are the emotions they produce from those which arise from the discoveries, miscalled improvements, in the savage art of war ; and what fond anticipations is the philanthropist led to indulge, of the early universal conversion of the sword and the gun into the plough-share and the reaping-hook, and of salt petre into a powerful manure.
Like all other new propositions offered for assent to the mind, those contained in Liebig's work will have to pass through the severe ordeal of the judgment, both of the experienced and of the inexperienced, both of the chemist and of the practical agriculturist, and much criticism has already been applied, and much opposition exhibited, to several of his doctrines. Still, no chemist of fixed reputation in Europe has yet ventured to assail the chemical principles there laid down ; and, if true, they will work their own way. With respect to the agriculturist, it must be remembered, that this book was written by a chemist for chemists, not by a farmer for farmers ; these last have yet something to learn,
before they can fully perceive the force of much of the reasoning, although they may readily apply to practice many
of the facts therein stated.
One of the most fertile themes of discussion has been the substance called humus, or geine ; whether in its complex state, or resolved, perhaps converted, into humic acid, crenic acid, apocrenic acid, &c. Now Liebig's statements appear simply confined to these assertions ;
First ; that humus is not present in fertile soils in a soluble form, as these soils do not yield any thing to cold water, except traces of inorganic salts. Humus, even in the most trifling quantity, would color the water brown, whereas water in which these soils have been digested, is completely colorless ; moreover, the juices absorbed by roots from these soils are also free from color. Admitting even that the humus of the soil were converted into humate of lime, the existence of which therein has, however, still to be proved, plants could only derive from this source a very small portion of the carbon they contain.
Secondly ; that on a given surface, either of woodland or meadow, from which large crops containing considerable carbon are annually removed without any replacement by manure, the soil becomes yearly richer in carbon under the form of humus or geine. These facts being demonstrated, it is scarcely possible to believe, that plants derive their carbon by absorption directly from humus or humic acid, an acid which, by the way, has never yet been discovered in soils, and is obviously a product of the decomposition of humus by alkalies.
We cannot doubt, that the true function of humus, or rather mould, is to yield a constant supply of carbonic acid to plants, when we are taught, by the beautiful experiments of Davy, that they decompose this gas large quantities.
So far is Liebig from denying the use of humus by his assertion that plants derive their great supply of carbonic acid from the atmosphere, that he merely asserts, that it does not act by direct absorption, but constitutes a source of carbonic acid, so constant, so gradual, so abundant, and, above all, so economical, that probably the utmost efforts of science will never discover one superior. Considered in this view, we cannot sufficiently admire the perfection of the provision, thus made by means so simple, for the abundant supply of the principal food of plants.
It is not worth while to notice the denial which has been made of the origin of nitrogen in plants from rain-water; the fact of ammonia existing in this medium, and in snow, having been sufficiently proved by scientific inquiry, both bere and in Europe ; nor need we defend the very evident origin of a considerable portion of this ammonia from the decay and dissolution (styled eremacausis by our author) of animal organization. This latter fact, indeed, forms an essential link in the wonderful chain of decay and reproduction, which it was one of his principal objects to trace, and which is so well delineated in the foregoing extract from the lecture of Dumas.
It is admitted, that Liebig does not claim to be the discoverer of the existence of ammonia in rain-water. This was known, even here, before his book appeared ; but he may justly claim the application of this and many other facts, which are now admiited without doubt into all considerations of vegetable physiology, such as the preservation of the purity of the atmosphere by the reproduction, by vegetables, of the oxygen consumed by animals, and the necessity of mineral or inorganic substances as food for plants. These, although to a degree known previously, have been placed by him in such new lights, and so many additional facts have been adduced, as have rendered them facts of sufficient certainty to guide the practical or experimental agriculturist. His statements concerning the amount of carbon annually removed from a given surface of ground in the shape of fuel, cannot be controverted ; and where the forests are, Germany, under the most rigid control and scientific management, his authority cannot be doubted.
With respect to guano, the analyses made by the chemists, to whom he refers, Klaproth, Vauquelin, Wohlen, and Boussingault, were certainly not made with the article in its fresh state ; and although it is not impossible, that this powerful manure may contain a portion of humus, yet this humus is not absorbed directly by plants; and, were humus the chief cause of the powerful effect of this inanure, there is yet more in inert peat mould.
Many of the most intelligent farmers in Germany have already testified to the value of the new views disseminated by Liebig, nor can it be much doubted, that, in proportion as they are spread here, they will be appreciated, and, as far as understood, applied practically.
The most valuable addition to this second edition is the extracts from the lectures of Dr. Daubeny on agriculture, in 1841, founded chiefly on this work of Liebig. In these, his principles, and their practical application, are fully discussed ; besides which, they contain the results of many experiments, undertaken as tests for the purpose of proving ihese principles.
These lectures are but the commencement of a history of the experiments, which are, or will be, instituted in all countries under the auspices of science, for the purpose of the economical increase of the produce of the soil ; a purpose launched forth into the broad ocean of human intellect by the writings of the present age, with an impetus far exceeding all our conceptions of material mechanics ; and which, in its course, gathering strength upon strength, bids fair not only to connect all mankind into one community of praise to the great Author of all for the simplicity, the beauty, the abundance of his works and his care, but to banish from the earth the mass of starvation and misery with which the unavoidable distinctions of poverty and riches seem almost to have overwhelmed its most fertile portions.
ART. XI.-CRITICAL NOTICES.
1. — Sir Henry Cavendish's Debates of the House of Com
mons, from May, 1768, to June, 1774 ; commonly called
“ The Unreported Parliament." It is known, that during an interesting period of British history, a period of six years from May, 1768, to June, 1774, no more than a very brief and meagre sketch of the debates in Parliament has been preserved. This blank was occasioned by a strict enforcement of the standing order for the exclusion of strangers from the gallery of the House. By a fortunate discovery, a series of manuscript reports of nearly all the principal debates during this period, taken down at the time by Sir Henry Cavendish, a member of Parliament has lately been brought to light. They are contained in forty-nine small quarto volumes. The discovery was made by Mr. J. Wright,