In these fifteen classes, one hundred natural orders are arranged; containing one thousand seven hundred and fifty-four genera. The characters of the genera are simple, and at the same time complete. The advantages of an increased number of characters are considerable, and it is not one of the least, that they are more simple, more easily comprehended and recollected.

The perfection of a natural method, is the philosopher's stone of the botanist. The great obstacle, says Linnaeus, is the number of plants not yet known. We have expressed a very opposite opinion, but with a different meaning. Linnaeus thought the method, which did not contain every vegetable, imperfect: he spoke of the groups, and the completion of a system, as comprehending the whole. But, as the shades by which nature varies her productions are minute and almost imperceptible, were every vegetable known, we should probably find discrimination into orders difficult, if not impossible. In the most natural orders, the distinction of genera is far from an easy task.

The arrangement of natural orders has occasioned some difficulty. From the varying shades by which these associations change, it has been proposed that they should follow each other according to their affinity. This is, however, difficult, and perhaps not the most convenient plan; for an order may agree with another in some respect, and with a very distant one in others. The idea suggested by Linnaeus, and executed, as we have said, by Giseke, is more convenient, viz. to lay them down like countries in a map, when the connection of the whole.vegetable kingdom will be obvious. As botanists now do not confine their descriptions to the arbitrary systematic distinctions only, natural systems will be daily more complete, and medical botany, we trust, be proportionably improved.

Though we look, however, to the perfection of a natural system as the best method of assisting our investigation of the medical properties of plants, we have expressed our approbation of an artificial one, as the most ready and convenient method of discovering the place of a vegetable in an arrangement of plants; and, of course, of obtaining a ready access to its synonyms. For these reasons we have identified the medicinal plants by a reference to the Linnaean system; and it remains to give some explanation of the principles on which the northern Pliny proceeded in constructing it.

Linnaeus was very early persuaded of the distinction of sexes in plants, a question now no longer disputed; for the last dart of Spalanzani 'rung, ineffectually tinkling on the shield.' The male organs he supposed to be the stamina; those upright filaments which, in a tulip or a lily, stand around a central column, bearing orange coloured bodies, the antherae. The central column is considered as the female organ, and styled the pistil, and its summit is the stigma. In the Linnaean system the first ten classes are distinguished by the number of the stamina, and styled monandria; diun-dria, etc. from the number of the or males. No vegetable contains eleven stamina, so that the eleventh class is distinguished by twelve dodecandria. The two next are those that contain twenty, or more than twenty, stamina, icosandria and po/yandria; but in these greater numbers there is not always a regularity, so that the attachment of the stamina to the calyx is afterwards superadded. The unequal length of the stamina distinguishes the two next classes. When of four, two are longer than the others, the class is styled didyna mia, the superiority of two; when of six, four arc longer, tetradynamia, the superiority of four. When the filaments of the stamina are united into one body, the class is styled monadelphia; when into two, diadel-fthia; when into many, polyadel/ihia, the brotherhood of one, two, or many; when united by the antherae, the class is syngenesia. When the stamina are attached to the pistil, the class is gynandria.

The sexual organs are sometimes found on different flowers of the same plant, sometimes on different plants. These furnish the monaecia and diaecia, a single or a double house. Sometimes they are found more indiscriminately, mixed with flowers which contain in one the organs of both sexes; and the class is then styled polygamia, many marriages. The last class contains the plants which have no visible flowers, the flags, the ferns, the mosses, and mushrooms; these are united under the class cryptogamia, concealed marriages.

Of these classes very few are natural: the tetrady-namia and monadelphia are very nearly such. The diadelphia and syngenesia do not contain many discordant plants.

The orders of the first thirteen classes are taken from the central column, which is not always a single one; and are styled monogynia, digynia, etc. from a woman. The orders of the didynamiae are distinguished by the seed being naked or covered; of the tetradynamiae, from the seed pod.

The classes distinguished by the connection of the stamina, are divided into orders from their number: those where the antherae are connected, from circumstances somewhat fanciful, but of little importance to explain. The orders of the gynandriae, monoeciae, and diocciae, are taken from the number and connection of the antherae, or their situation. Those of the polygamiae from the flowers being on the same, or on different plants. The orders of the cryptogamiae are the natural families formerly mentioned; and to these Linnaeus adds the natural family of the palmae.

Of the numerous vegetables thus arranged, but few are used in medicine; and it has been for ages the subject of declamation, echoed from mouth to mouth with little change, and with little discrimination, how improperly we employ chemical medicines which the stomach cannot assimilate, instead of vegetables which are subservient to its power. We arc not yet prepared to discuss this question; yet we have already found that the vital fluid is seldom greatly changed in the most violent diseases; and in many no change has been even suspected. The great sources of disease are the excess and diminution of motion, or irregular action; producing either spasmodic paroxysms, or a de-rangement of the balance of the circulation. In a few instances only are the fluids affected; and in the greater number of these the fault is corrected by exciting the action of the moving powers, rather than amending the supposed deterioration. Yet we mean not to reject or undervalue vegetable medicines: in many instances are our great support. Nor can we find, in the mineral kingdom, medicines equal to ipecacuanha, to rhubarb, the different aromatics, and, perhaps, the bark. Were we to pursue the list, it would not, however, fill many lines. In a vignette to the Materia Medica Con-tracta of Tessari, though we believe the original idea was Haller's, we see two boys holding the 'sieve of truth.' Opium, castor, and bark, only fall through; the rest are retained, even the radix senckae; and cinnabar is seen apparently forcing a passage.