plants referable to different families will not graft on each other, apparently, because the juices elaborated in different families of plants, though growing side by side, in the same soil, are so different in their qualities that those of the one are unfit to nourish a branch taken from the other : while on the other hand two plants of the same natural family, however much the soils in which they respectively grow may differ, can generally, be readily grafted on each other. From the same cause, the action, namely, of organization on secretion, we find in a great many instances identical properties common to whole families of plants. Acrimony predominates throughout the Ranunculaceae and Cruciferae : narcotism is the characteristic of Papaveraceae and Solanaceae : Apocyneae are generally poisonous and some of the species most virulently so : astringency is common to nearly all the arboreous Mimoseae as well as to many of the Caesalpineae, it equally predominates in Terminaliae, and the whole of the genus Quercus is pre-eminently marked by that property. The Cucurbitaceae, Convolvulaceae and Euphorbiaceae are equally distinguished by properties the very reverse, the action of many species of each of these orders being violently drastic. The fruit of Rosaceae and seed of Leguminosae on the contrary, are so universally wholesome that it may be laid down as a general rule almost without exceptions, that they may be safely partaken of whenever they are met with.
These few examples will suffice to show how vastly the study of properties is facilitated by an acquaintance with natural affinities, and will, I trust, at the same time serve to remove an objection which I have more than once hard urged against this work, that it did not sufficiently treat of Medical Botany. This objection could only be raised by those who did not sufficiently consider that its object was to establish principles on a scientific basis, as being the true way to attain the object sought for. There is no royal road to science, and until the medical man studies the principles of Botany as a science, he need never expect through an inspection of plates or specimens of medical plants to become a medical Botanist. But with only an elementary knowledge of Botany, such for example as a perfect knowledge of the structure of the flower and fruit, an acquisition not generally of very difficult attainment, the case is widely altered, since any one who had advanced so far in the knowledge of the elements of the science may easily make himself master of the characters of a few species of an order, and then he can generally trace its relations with nearly allied orders or even recognize some of them from family likeness alone. Having ascertained the order of the plant under examination the subsequent steps leading to the attainment of a comprehensive knowledge of its name, history and properties, are comparatively easy; and not of it only but of the whole order. It is true, that to acquire a thorough acquaintance with an order, frequently requires the student to examine and carefully compare several, but every plant so examined facilitates subsequent researches and lessens the difficulty of the next step, that namely of making out the genus. But even without going so far, having once determined the order of a plant, we are in possession of a fund of information, since, but little further trouble is required to make ourselves acquainted with all that is yet recorded respecting that order, and to ascertain whether any applications we have learned are still unknown to science. The natural method in short gives both precision and extension to any enquiries we may undertake respecting plants, whether considered with reference to organic structure and its modifications, the products of organic life in connection with structure, or the applications of these products to the comforts and conveniences of life; and thereby to the advancement of civilization among men. The difficulties to be surmounted at the outset of the study are no doubt often great, those namely.
