Loudon's Encyclopædia of Gardening. 37 empire. It is pleasing also to be able to state, that Mr. Loudon has availed himself of the best and latest sources of information on the various subjects concerning which he treats, and that modern science and discriminating judgment, are here properly and ingeniously combined. Although a cyclopædia, it is not alphabetically arranged; and, indeed, the alphabetical arrangement would by no means suit the nature of the subject, nor the materials here brought together. We, therefore, cannot but highly approve the arrangement which the author has adopted. The first part treats of gardening considered in respect to its origin, progress, and present state among different nations, governments, and climates; this is subdivided into the history of gardening among ancient and modern nations; and gardening considered as to its progress and present state under different political and geographical circumstances.-The second part treats of gardening considered as a science: this is subdivided into the study of the vegetable kingdom; of the natural agents of vegetable growth and culture; mechanical agents employed in gardening.-The third part treats of gardening as practised in Britain: this is subdivided into Horticulture, Floriculture, Arboriculture or planting; and Landscape gardening.-The fourth part consists of the statistics of British gardening these are subdivided into the present state of gardening in the British Isles; and on the future progress of gardening in Britain. To these are added a kalendarial and a general index. The woodcuts by Branston are useful and explanatory; many of them are ornamental: they much enhance the value of the volume. The practical articles for the professor, as well as the gentleman gardener, are at once numerous and useful; for these we must refer the reader to the work itself. We might, indeed, have presented our readers with the articles inarching, grafting, budding, &c., as samples of the work, which are clear and explicit; but must deny ourselves that pleasure to make room for another on the process of vegetable nutrition, which we recommend to the diligent perusal of a quondam friend of ours, who is fond of talking on the subject, as well as, also, to the attentive consideration of our readers. The articles inarching, grafting, &c., are elucidated with woodcuts very explanatory of the different processes. Mr. L. tells us that shield budding reversed, L, is now generally considered exploded. We confess that this news surprizes us. We ask, with due submission, how long has it been so, and by whom? If we have any complaint to make of Mr. Loudon's work, it is, that it is rather too technical; but it is difficult to please readers of every taste and degree of knowledge. Process of Vegetable Nutrition. "Elaboration of Oxygen It has been already shown that the leaves of plants abstract oxygen from confined atmospheres; at least, when placed in the shade, though they do not inhale all the oygen which disappears;` and it has been further proved, from experiment, that the leaves of plants do also evolve a gas in the sun. From a great variety of experiments relative to the action and influence of oxygen on the plant, and the contrary, the following is the sum of the results. "The green parts of plants, but especially the leaves, when exposed in atmospheric air to the successive influence of the light and shade, inhale and evolve alter Process of Vegetable Nutrition. 89 nately a portion of oxygen gas mixed with carbonic acid. But the oxygen is not immediately assimilated to the vegetable substance; it is first converted into carbonic acid, by means of combining with the carbon of the plant, which withers if the process is prevented by the application of lime or potass. The leaves of aquatics, succulent plants and evergreens consume, in equal circumstances, less oxygen than the leaves of other plants. The roots, wood, and petals, and in short, all parts not green, with the exception of some coloured leaves, do not affect the successive and alternate inhalation and extrication of oxygen; they inhale it indeed, though they do not give it out or assimilate it immediately; but convey it under the form of carbonic acid to the leaves, where it is decomposed. Oxygen is indeed assimilated to the plant, but not directly, and only by means of the decomposition of carbonic acid; when part of it, though in a very small proportion, is retained also, and assimilated along with the carbon. Hence the most obvious influence of oxygen as applied to the leaves, is that of forming carbonic acid gas, and thus presenting to the plant elements which it may assimilate; and, perhaps, the carbon of the extractive juices absorbed by the root, is not assimilated to the plant till it is converted, by means of oxygen, into carbonic acid. But as an atmosphere, composed of nitrogen and carbonic acid gas only, is not favourable to vegetation, it is probable that oxygen performs also some other function beyond that of merely presenting to the plant, under the modification of carbonic acid, elements which it may assimilate. It may effect also the disengagement of caloric by its union with the carbon of the vegetable, which is the necessary result of such union. But oxygen is also beneficial to the plant from its action on the soil: 1 for when the extractive juices, contained in the soil, have become exhausted, the oxygen of the atmosphere, by penetrating into the earth and abstracting from it a portion of its carbon, forms a new extract to replace the first. Hence we may account for a number of facts observed by the earlier phytologists, but not well explained. Du Hamel remarked that the lateral roots of plants are always the more vigorous, the nearer they are to the surface; but, it now appears, that they are the most vigorous at the surface, because they have then the easiest access to the oxygen of the atmosphere, or to the extract which it may form. It was observed, also by the same phytologist that perpendicular roots do not thrive so well, other circumstances being the same, in a stiff and wet soil, as in a friable and dry soil; while plants, with slender and divided roots, thrive equally well in both: but this is no doubt owing to the obstacles that present themselves to the passage of the oxygen in the former case, on account of the greater depth and smaller sur-face of the root. It was further observed, that roots which penetrate into dung, or into pipes conducting water, divide into immense numbers of fibres, and form what is called, the fox-tail root; but it is, because they cannot continue to vegetate, except by increasing their points of contact, with the small quantity of oxygen found in such mediums. Lastly, it was observed, that plants, whose roots are suddenly overflowed with water, remaining afterwards stagnant, suffer sooner than if the accident had happened by means of a continued current. It is, because, in the former case, the oxygen contained in the water is soon exhausted, while, in the latter, it is not exhausted at all. And hence, also, we may account for the phenomenon exhibited by plants vegetating in distilled water, under a receiver filled with atmospheric air, which having no proper soil to supply the root with nourishment, effect the developement of their parts only at the expense of their own proper substance; the interior of the stem, or a portion of the root, or the lower leaves decaying, and giving up their extractive juices to the other parts. Thus it appears that oxygen gas, or that constituent part of the atmospheric air, which has been found indispensable to the life of animals, is also indispensable to the life of vegetables. But although the presence and action of oxygen is absolutely necessary to the process of vegetation, plants do not thrive so well in an atmosphere of pure oxygen, as in an atmosphere of pure and common air. Whence it follows, that oxygen, though the principal agent in the process of vegetation, is not yet the only agent necessary to the health and growth of the plant; aud that the proportion of the constituent parts of the atmospheric air, is well adapted for the purposes both of vegetable and animal life." Polytechnic and Scientific Intelligence. Society of Arts. PUBLIC exhibitions are the order of the day. To this, however, we have no kind of objection, provided they tend to some beneficial purpose. The rooms of the Society of Arts, being inconvenient for the appropriate distribution, before a numerous audience, of the medals and premiums adjudged during the year, it was thought desirable to obtain the use of Drury-lane Theatre for the purpose. And on Wednesday, the 29th of May, the |