"It is not necessary here to give any detailed account of the terms of botany. The fundamental ones have been gradually introduced, as the parts of plants were more carefully and minutely examined. Thus the flower was necessarily distinguished into the _calyx_, the _corolla_, the _stamens_, and the _pistils_; the sections of the corolla were termed _petals_ by Columna; those of the calyx were called _sepals_ by Necker. Sometimes terms of greater generality were devised; as _perianth_, to include the calyx and corolla, whether one or both of these were present; _pericarp_, for the part enclosing the grain, of whatever kind it be, fruit, nut, pod, &c. And it may easily be imagined, that descriptive terms may, by definition and combination, become very numerous and distinct. Thus leaves may be called _pinnatifid_, _pinnatipartite_, _pinnatisect_, _pinnatilobate_, _palmatifid_, _palmatipartite_, &c., and each of these words designates different combinations of the modes and extent of the divisions of the leaf with the divisions of its outline. In some cases, arbitrary numerical relations are introduced into the definition: thus, a leaf is called _bilobate_, when it is divided into two parts by a notch; but if the notch go to the middle of its length, it is _bifid_; if it go near the base of the leaf, it is _bipartite_; if to the base, it is _bisect_. Thus, too, a pod of a cruciferous plant is a _siliqua_, if it is four times as long as it is broad, but if it be shorter than this it is a _silicula_. Such terms being established, the form of the very complex leaf or frond of a fern (Hymenophyllum Wilsoni) is exactly conveyed by the following phrase:--'fronds rigid pinnate, pinnæ recurved subunilateral, pinnatifid, the segments linear undivided or bifid spinuloso-serrate.' "Other characters, as well as form, are conveyed with the like precision: Colour by means of a classified scale of colours.... This was done with most precision by Werner, and his scale of colours is still the most usual standard of naturalists. Werner also introduced a more exact terminology with regard to other characters which are important in mineralogy, as lustre, hardness. But Mohs improved upon this step by giving a numerical scale of hardness, in which talc is 1, gypsum 2, calc spar 3, and so on.... Some properties, as specific gravity, by their definition give at once a numerical measure; and others, as crystalline form, require a very considerable array of mathematical calculation and reasoning, to point out their relations and gradations." § 3. Thus far of Descriptive Terminology, or of the language requisite for placing on record our observation of individual instances. But when we proceed from this to Induction, or rather to that comparison of observed instances which is the preparatory step towards it, we stand in need of an additional and a different sort of general names.