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vegetation. It is evident, therefore, that the additional layer by which the plant increases in diameter is generated from the burk.' 11. pp. 218-220.
A further question, of considerable physiological interest, arises : Is the new layer thus formed, merely the indurated Liber of the former year; or is it a perfectly distinct substance, secreted by the bark, but not produced by the conversion of the bark into wood? From some delicate experiments of Du Hamel, it appears certain that the bark acts only as the organ of transmission of the secreted fluid, and that the new layer of wood is formed by the descent of the proper juice (or Cambium as named by Du Hainel) from the leaf through the vessels of the bark. It is highly probable, also, that this gelatinous substance, or fluid of organization, is secreted in two distinct concentric layers; one tending to the centre, and forming the Alburnum, or new wood, the other tending to the circumference, and constituting the Liber, or young bark.
Our limits forbid us to enter, at any length, upon the amusing part of these volumes, which treats of the products of vegetable Analysis. In the Section upon Resins,' we have the following notice, resting on the authority of Mirbel, respecting the Bloom, which is vulgarly attributed to the presence of animalcule.
Upon the epidermis of the leaves and fruit of certain species of plants, there is to be found soft and glaucous powder. It is particularly observable upon cabbage leaves, and upon plums, to which it communicates a peculiar shade. It is known to gardeners by the name of bloom. It is easily rubbed off by the fingers; and when viewed under the microscope seems to be composed of small opaque and unpolished granules, somewhat similar to the powder of starch; but with a high magnifying power it appears transparent. When rubbed off, it is again reproduced, though slowly. It resists the action of dews and rains, and is consequently insoluble in water, But it is soluble in spirits of wine; from which circumstance it has been suspected, with some probability, to be a Resin." Vol. I. p. 438. See also p. 187 .
Among the Gum-Resins, (which are obtained from vegetables by expressing and inspissating the juice, not by natural exudation, we meet with the pigment so familiarly known in every drawing-box, under the name Gamboge. This substance exudes from incisions in the back of the East Indian tree Mangostana Cambogia. The disagreeable Assafætida (the concreted milky juice of the Persian Ferula assafætida) is also a Gum-Resin; which, however uninviting to Europe
tastes, from its intolerably fetid odour, is used by the Indians as a seasoning for their food, and is called by them the food of the gods. With this we may contrast a Gum-Resin of more inviting character-Myrrh : it is concreted, in the form of tears, from
some unknown Abyssinian and Arabian plant, which Bruce refers to the Genus Mimosa ; it is supposed to be the Acacia vera, or, as it has been called by some Botanists, the Mimosa Nilotica, the Egyptian Thorn.
Many vegetables are known to secrete Wax, in a form very little adulterated by extraneous substances. It esudes from the fruit of Myrica cerifera, Common American Candle-bury Myrtle, a plant which grows abundantly in Louisiana. The beautiful and singular phenomenon exhibited by the Dictamnus albus, or White Fraxinella, is supposed to be owing to a perspi. ration of Was, which forms an inflammable atmosphere around
This plant is fragrant, and the odour which it diffuses around forms a partial and temporary atmosphere which is inflammable; for if a lighted candle, or other ignited body, is brought near to the plant, especially in the time of drought, its atmosphere immediately takes fire. This phenomenon was first observed by the daughter of the celebrated Linnæus, and is explained by supposing the partial and temporary atmosphere to contain a portion of Was exuded from the plant, and afterwards reduced to vapour by the action of the sun.' I. p. 428.
Wax is found in different plants in various states of concretion. When it has the consistency of butter, it is denominated Butter-of-Wax. The Butter of Cacao is expressed from the seeds of Theotroma Cacao, the Smooth-leaved Chocolate Nuttree: it is to this substance that chocolate owes its flavour and unctuosity.
Our last quotation shall be upon the useful substanco Caoutchouc, more familiarly known by the name IndianRubber.
• It is obtained chiefly from Harvea Caoutchouc and Jatropha elastica (the Elastic Physic. Nut], trees indigenous to South America ; bus it has been obtained also from several trees which grow in the East Indies, such as Ficus Indica [the Banyan-tree), Artocarpus inteSrifolia (the Indian Jaca-tree), and Urceola elastica [a native of Prince of Wales' Island, and the coast of Sumatra].
• If an incision is made into the bark of any of these plants a milley juice exudes, which, when it is exposed to the air, concretes and forms Caoutchouc. As the object of the natives in collecting it had been originally to forin it into vessels for their own use, it is generally made to concrete in the form of bags or bottles. This is done by applying the juice when fluid, in thin layers, to a mould of dried clay, and then leaving it to concrete in the sun or by the fire. A second layer is added to the first, and others in succession, till the vessel acquires the thickness that is wanted. This mould is then broken, and the Vessel fit for use, and in this
state it is generally brought into Europe. It has been brought, however, even in its milky state, by being con. fined from the action of the air....isé
• Caoutchouc, when pure, is of a white colour, without taste, and without smell. The black colour of the Caoutchouc of commerce is owing to the method of drying the different layers upon the moulds on which they are spread. They are dried by being exposed to smoke.......
• It seems to exist in a great variety of plants combined with other ingredients. It may be separated from resins by alcohol. It may be separated from the berries of the Misletoe by means of water, and from other vegetable substances by other processes. It is said to be contained both in opium and in mastic. But from these substances it cannot be extracted in sufficient quantities to make it worth the labour. It is applied to a great many useful purposes both in medicine and in the arts, to which, from its great pliability and elasticity, it is uncommonly well-adapted. In the countries where it is produced the natives make boots and shoes of it, and often use it by way of candle.' I. pp. 449–451.
Here we must close our extracts from the interesting matter of these volumes. It only remains for us to give our readers some information respecting the general merit of the work; and in doing this, our remarks shall be brief, because, from the general outline, and from the copious quotations which we have brought before them, a tolerably correct idea may be formed of what may be expected in the perusal of the whole. We do not hesitate in declaring our opinion that, in its general execution, it is highly creditable to Mr. Keith, and that it is well adapted both to advance his own reputation in the scientific world, and to promote the extension of knowledge in this department of Natural History. Very few facts with which we were not previously acquainted, are brought forward by Mr. Keith ; but his materials are drawn from the best sources, and he has given a comprehensive statement of the principal physiological phenomena in the vegetable creation, which are scattered throughout many volumes in the works of Linnæus, Grew, Bonnet, Hedwig, Du Hamel, Malpighi, Mirbel, Ellis, Knight, and many other philosophical writers upon the anatomy and functions of plants. It is always a somewhat invidious task to contrast rival works, by different living writers, each of which possesses its peculiar merits ; we cannot, however, withbold an opinion, to the declara. tion of which the readers of our Review are, perhaps, entitled, that Mr. Keith's treatise by no means supersedes the elegant volume upon Physiological Botany, by the President of the Linnæan Society, although the latter is condensed into one half of the bulk of the former. In Dr. Smith's work there is a touching 'vimplicity of style, a delicacy of expression, and an exquisite selection of illustrations, which have rendered his book a classical volume, and which will continue to ensure it a place in the library of every person of taste and science. In Mr. Keith's volumes there is more detail, which is not without its advantages;
but we think he has not always been judicious in swelling liis pages with a list of unsuccessful physiological experiments, when he should rather have seized upon the points of fallacy, and given us the general results, without entering into a tedious enumeration of the actual processes of indecisive trials. If this method of proceeding renders his work somewhat less attractive to the merely popular reacler, it may possibly give an increased value to it as a inanual for the wore patient student in Physiological Botany. There are some subjects, and those not the least interesting, in these volumes, which are scarcely at all touched upon by Dr. Smith. Among these, the part which is devoted to Chemical Botany, or the Analysis of Vegetable Products, will be found to contain a vast fund of valuable information ; but even in this department we cannot commend the extreme minuteness of detail which often leads Mr. Keith far from his subject. Who, for instance, would expect, in a treatise on Physiological Botany, to meet with the information, tbat the best Flint Glass is composed of 120 parts of white siliceous sand, * 40 parts of pearl-ash, 35 of red oxide of lead, 13 of nitrate of potass, and 25 of black oxide of manganeze?" Vol. I. p.
460. The mere circumstance that the vegetable alkali is used 1 in the manufacture of glass, is too slender a link to sustain such
digressive details, for if such be allowed, they become positively I interminable.
Some other faults have been noticed by us, and must not be i passed over without remark. The numerous subdivisions
of the treatise are so far froin contributing to the ' lucidus 'ordo,' that they perplex by the intricacy of their ramifications. To say nothing of ihe division into Volumes, which is one of merely mechanical convenience,' we have Books, Parts, Chapters, Sections, Sub-sections, and Articles, in a descending series. The extremely subtle divisions of his materials, produces, as a natural consequence, both intricacy and repetition : thus we have observed that the account of the Bloom is repeated Vol: I. p. 187 and p. 438; the curious phenomenon of the Dictamnus albus occurs twice, Vol. I. p. 428 and Vol. II. p. 119; and we meet with the very same observations on the Colthorpe Oak at two remote intervals Vol. I. p. 48 and Vol. II. p. 506; &c. &c. We think that those parts which are merely descriptive of the parts of plants, and their various forms, miglit be much more conveniently thrown into the shape of a Catalogue, as in Dr. Smith's work, by which means much heaviness of style would be avoided : by adoptivg the contrary plan, Mr. Keith has been compelled to link his sentences together by the perpetual use of particles repeated to satiety.
Our report of this work having been, as we conceive, sufficiently extended, we pow dismiss it, not without a favourable
VOL. IX.N.S... 2 D
opinion, and a cordial hope that many who have read this critique will becoipe better acquainted with the pages on which it is a comment; for we are confident that, whether they be popular or scientific readers, they will not rise from their perusal without much amusement and instruction.
Art. III. A Voyage round Great Britain, undertaken in the Summer
of the Year 1813, and commencing from the Land's End, Cornwall : by Richard Ayton. With a Series of Views, illustrative of the Character and prominent Features of the Coast, drawn and engraved by William Daniell, A.R.A. Imperial 4to. Vols. I and
II. pp. 440. Price, half-bound, £15. 1814, 15, 16.* [Fifty-five Views, coloured, and a Vignette.] IT T is very fairly made, in the preface to this work, a matter
of wonder, that all the numerous and diversified undertakings for the topographical illustration of our island, should have left to a describer and delineator, so late in the day, a subject of absolute novelty in a comprehensive survey of its coast. cepting the fashionable watering-places, some of the ports, and a few remarkable picturesque points, (not, however, for the most part, satisfactorily delineated, the coast is an unknown region to even the most topographically given of the many readers whom it encircles.
• It is the design, therefore, of the following Voyage, minutely to describe the whole coast round Great Britain ; not merely to give plans and outlines of its well-known towns, ports, and havens ; but to illustrate the grandeur of its natural scenery, the manners and employment of people, and modes of life, in its wildest parts.'
* As in this voyage the reader will find two navigators frequently sailing on horseback, and on more than one occasion scudding in a gig, it will be necessary to explain the causes which obliged them to prosecute their course by means so irregular and unfamiliar. When the undertaking was first designed, the authors most certainly intended to travel principally by sea, but, on experiment, the plan was found to be utterly impracticable. As it was their object to examine every point, and stone, and cranny of the coast, no kind of boat was calculated for their service but a small rowing boat, as no other could venture to approach near enough to the shore for their purposes. The boat was easily to be procured, but the winds and waves were not so tractable: rapid tides, ground-swells, insur
* The work has been published, and continues to be published, in monthly numbers, twenty-eight of which, containing each two plates, at the price of 10s. 64. constitute these first two volumes. All the numbers subsequent to the termination of the second volume contain, at the same price, each three plates, but with a smaller proportion of letter-press. On this plan the work is intented to continue.