Art. V. A System of Physiological Botany; illustrated by Nine Engravings. By the Rev. P. Keith, F. L. S. Vicar of Bethserden, Kent; and Perpetual Curate of Marr, Yorkshire. In Two Volumes, 8vo. pp. 1004. Price £1. 6s. London; 1816.

THE

HE astonishingly rapid progress which has been made in the Arts and Sciences, during the last two centuries, is to be attributed mainly to the inductive method of investigation, in which our immortal Bacon laid the basis of a solid Philosophy. There is, however, another collateral cause of the advancement of human knowledge, and which naturally arose out of the rigid principles of the Baconian method; we mean, the distribution of the objects of our speculations into distinct departments. The intellectual advantage derived from pursuing such a method, is not dissimilar to the improvements which have taken place in mechanical operations, by the division of labour; a facility of research, and a more accurate perception of truth, are naturally attendant upon the practice of viewing subjects, not in a confused mass, but arranged under certain classes. When we are pursuing a certain order of facts, with a particular reference to well-defined objects of investigation,-excluding such as fall not immediately within the scope of our searches, not only is the attention riveted more closely to the phenomena which come under our notice, but truth itself is displayed to our observation, with a greater force and simplicity. 'Science' (as Lord Bacon has remarked) is only 'the image of truth.' We may extend this just observation, by the remark that truth, when presented to the mind in all its involved combinations, without method, reaches our intellectual faculties as so many scattered rays would reach the optic nerve, producing no impression which bears a nice correspondence with the simple phenomena of nature: but truth, when viewed under a perfect distribution of its parts, leaves a welldefined idea in the mind;-its rays, instead of being dispersed in a confused flood of light, are gathered into their appropriate pencils, converge to their respective foci, and paint a mental image, exquisitely conformable to the actual object in the examination of which we are employed.

*

re

To say nothing more upon the very great advantages which have been derived from a methodical distribution of the objects of our speculations, in other departments of human knowledge, it must be manifest, to every thinking person, that our disco

*Of course we shall not be understood as using this word with reference to Mr. Locke's exploded theory of ideal images; we merely adopt it to express the correspondence which exists between the perception of truth, and truth as an essence independent of our knowledge. Scientia nihil aliud est quàm veritatis imago, nam veritas essendi, et veritas cognoscendi, idem sunt.'

veries in the physical sciences have been rapidly promoted by this circumstance; the investigations of philosophers having been conducted, in modern times, with reference to particular classes of phenomena, instead of having been pursued in the general, discursive, confused manner of most of the ancient writers upon such subjects, All our researches into the kingdoms of nature may evidently be classed, with convenience, under two grand divisions,--the systematical, and the analytical methods. The artificial or systematical method, leads us to view the various objects of nature with reference, principally, to their external characters. Its chief importance consists in enabling us to arrange the materials of our contemplations into distinct families, so that each individual object may be perspicuously described, and accurately distinguished from every other in creation. The analytical method, is conversant with the constituent principles of mutual relation of the parts of bodies. It leads us to consider the affinities of Elementary proportions by which the particular conformation of the individual is determined, or the various functions upon which the phenomena connected with its existence depend. If the subject of our investigations be matter endowed with organization and vitality, the analytical method resolves itself into a physiological inquiry; by which is meant, an investigation of the causes by which the phenomena exhibited by animated or simply organ ized matter are produced, and of the laws by which it is governed,-involving of course, a more intimate examination of its structure than would be necessary for, or even applicable to, the purposes of merely systematical arrangement.

In Botanical Science we have abundant proof of the advantages derived to philosophy from the separation of these two distinct objects of inquiry. By the ancients it was thought sufficient to treat of vegetables in the mass, without pursuing any very definite line of inquiry. Hence, their individual characters, their functions, their properties, their medicinal virtues, their habitat, were all blended together in one rude description; it is not therefore surprising, that (however valuable may be the incidental information which we desire from their works) very little has come down to modern times from these ancient sources in the form of scientific discovery. Systematical Botany was a science in its very infancy, so late as the middle of the sixteenth century; for the first ideas which deserve the appellation of Botanical arrangement, were communicated, at that period, almost cotemporaneously, by Gessner in Switzerland, and by Casalpinus in Italy. Vegetable physiology seems to have been almost uncultivated until a century later, when our countryman Dr. Nehemiah Grew, and Marcellus Malpighi, a Bolognese, reaped the first fruits of a field which has since yielded an abundant harvest. Since the time of these indefatigable na

turalists, what a prodigious stock of phytological information has been contributed by the labours of Bonnet, of Du Hamel, of Gærtuer, and, still more recently, of Mirbel, of Humboldt, and of (our own countrymen) Knight and Eilis!

In pursuing our studies in any particular department of science, to whichever of the two great branches above-mentioned our faculties may be applied, we shall find much to interest us. A knowledge of a science, systematically, is, no doubt, the first acquisition in point of order; since it is by this method alone, that we can either ourselves become acquainted with the individual characters of the objects of our study, or communicate our ideas to others. Much of the power and the wisdom of the Creator, is necessarily unfolded to our view, even when our contemplation of his works is limited to their external conformation, and their more obvious characters. Physiological science is, however, a pursuit of a still higher and more dignified order: while engaged in the investigations to which it conducts, we enter the great laboratory of nature; we lift the veil which hides, from the merely general observer, her more secret and refined operations; we gaze upon the exquisite machinery by which she is preparing, unseen, the fairest of her tints, and the most delicate of her dresses; and, if we are Christian Philosophers, we shall ever rise from such interesting speculations (not with a vain conceit of the self-agency of material causes, but) deeply impressed with the all-pervading action of that Invisible Hand, which arrays "the lilies of the field" with a greater glory than Solomon's, though "they toil not, "neither do they spin!"

There is yet another decided advantage which we derive from physiological pursuits, and which is not to be reaped from a merely systematic knowledge. Pursuits of the latter class more immediately lead us to contemplate the objects of nature in their individual characters; in Botany, e. g. it is the difference which we trace between two genera or two species, which teaches us to distinguish them from each other. Investigations of the former description lead us, on the contrary, to a more enlarged view of nature, to the recondite analogies which exist between individuals far removed from each other in the systematical arrangement, and differing widely in their external character. We cannot but observe a similarity of functions, of laws, of properties, and of anatomical structure, which links together individuals which we might scarcely have imagined to be connected by any common chain; nor are these physiological analogies confined to a correspondence between the objects of any one department of nature; they are more or less to be traced between many of the works of creation, which, in other respects, are separated from each other by distinct lines of demarcation.

They form, in fact, the harmonies of nature; and they unfold to us the interesting truth, that the most pleasing and inexhaustible variety in the works of God, is not inconsistent with a certain simplicity of design, and uniformity of action, in the laws by which they are governed. As we admit, however, that the love of tracing natural analogies has often given rise to absurd and fanciful speculations, we must beg permission both to guard our remark with some few cautions, and to obviate an objection which has been urged against one of the most interesting of physiological pursuits.

The propensity to trace real or fancied analogies between the different systems of nature, may be remarked in the history of every science. Such analogies have, sometimes, been founded upon the weakest, and even the most absurd hypotheses. When this is the case, it cannot be doubted that such a method of investigation has a tendency to retard rather than promote the advancement of human knowledge. The very love of our adopted theory, may lead us to reject many facts, as unimportant or doubtful, because they do not conform to the favourite analogy which we have imagined to exist between two particular departments of science; although these facts, had they been pursued, without bias, to their legitimate consequences, would have conducted us to some of the most valuable conclusions. A physiological investigator cannot, therefore, be too much upon his guard, lest he should suffer his fancy to rove without reasonable control, over this enchanting ground; for, undoubtedly, the analogies and harmonies which subsist between objects, which at first consideration appear to be placed in the most opposite parts of the system of nature, constitute some of the most inviting subjects of philosophical study. At the same time it must, we think, be allowed, that the very propensity which is so liable to be abused, is also capable of being made subservient to the most valuable and sublime investigations. The very analogies which he has actually discovered, or has imagined to exist, communicate an ardour to the mind of the investigator, which might otherwise have never been imparted; the stimulus, when once excited, carries him through many uninviting parts of his subject, upon which he might never even have entered in the simple pursuit of an insulated truth. In fact, however little attachment we might originally have felt for the immediate subject of investigation, the analogy is the offspring of our own mind, and as such we cannot but cherish it; and while we are impelled forward by the desire of establishing our favourite hypothesis, we are necessarily led to view nature in forms under which she might never otherwise have presented herself to our notice. Thus we are insensibly led to the knowledge of phe

nomena for which, perhaps, we were not in search, and which, probably, we did not even suspect to exist.

Of the truth of these remarks we cannot forbear noticing a striking instance, in the progress of discovery respecting the laws of the planetary system. Who shall say that the rude analogy which the ancients fancifully supposed to exist between the harmony of the heavenly spheres, and the intervals of a musical chord, did not give the first impulse to those speculations which terminated in the beautiful system established by the Newtonian philosophy? It was in the pursuit of planetary analogies, (somewhat more philosophical, but not less erroneous, than these,) that the great Kepler actually discovered the laws by which the heavenly bodies are governed. He set out upon the false hypothesis of the ancient philosophers, that the path of a planet must be the most simple of all geometrical curves, the circle in the very endeavour to establish his favourite but false position, he discovered the elliptic orbits. He fancifully imagined that a certain analogy existed between the distances of these masses from the sun, and their respective revolutions around his centre. In the progress of investigation he learned the beautiful fact, that though his own analogy was not the law of nature, yet a real analogy did exist;-the cubes of the periodic times being proportional to the squares described upon the mean distances. Kepler was led, by his pursuit of harmonies, to trace the actual conditions of the planetary orbits; and thus he prepared the way for the physical demonstrations of Newton, who succeeded in establishing the law of universal gravitation.

But we return from this digression, to that particular science to which this article is devoted. Botany is not less indebted to analogies, than astronomy. It was the analogy which Linnæus observed between many of the functions of animals and vegeta. bles, that led him to adopt the sexual system, as the most perfect for classification; and whatever may be thought of the actual harmony which subsists between these two departments of creation, it led to the observation of certain facts, intimately connected with the structure of plants, and most important for the purposes of artificial arrangement. In the physiological part of the science, analogies of the most interesting kind present themselves to our notice, and have always been pursued with avidity, by writers upon the subject. We are not, indeed, among those who imagine that a natural barmony exists between the joints in the stalk of corn, and the number of lunar months which have elapsed between the germination of the seed, and the maturity of the plant; but, undoubtedly, there are many analogical phenomena worthy of notice; they constitute,