It is also in a great degree true that the sensible qualities of plants, such as _colour_, _taste_, and _smell_, have an intimate relation to their properties, and may often lead by analogy to an indication of their powers; we have an example of this in the dark and gloomy aspect of the _Luridæ_, which is indicative of their narcotic and very dangerous qualities, as _Datura_, _Hyoscyamus_, _Atropa_, and _Nicotiana_. _Colour_ is certainly in many cases a test of activity; the deepest coloured flowers of the _Digitalis_, for example, are the most active, and when the leaves of powerful plants lose their green hue, we may conclude that a corresponding deterioration has taken place with respect to their virtues; but Linnæus ascribed too much importance to such an indication, and his aphorisms are unsupported by facts; for instance, he says “Color pallidus _insipidum_, viridis _crudum_, luteus _amarum_, ruber _acidum_, albus _dulce_, niger _ingratum_, indicat.”[87] A peculiar heavy odour, which is well known, but is with difficulty defined, is a sure indication of narcotic properties. Bitterness, when not extreme, denotes a tonic quality, which will stimulate the stomach and intestines, and promote the process of digestion. When the bitterness is more intense and pungent,[88] as in _Aloes_, _Colocynth_, _&c._ we may infer that such substances will produce a more active effect upon the _primæ viæ_, and that catharsis will follow their administration. Botanical, like human physiognomy, may frequently afford an insight into character, but it is very often a fallacious index. With regard to the indications of _Smell_ and _Taste_, it may be observed that in the examination of an unknown substance we instinctively apply to these senses for information respecting its properties. It is certainly reasonable to suppose, that those bodies which produce upon the organs of taste a sensible, astringent, or pungent effect, may occasion an impression, corresponding in degree upon the stomach or intestines, which are but an extension of the same structure. But what numerous exceptions are there to such a law? nay, some of the most poisonous substances affect in a very slight degree the organs of taste, especially those that belong to the mineral kingdom, as _Arsenious Acid_, _Oxyd of Antimony_, _Calomel_, _&c._; yet some of these are, perhaps, but apparent exceptions, depending upon the degree of solubility which they possess, in consequence of which their energies are not developed until they have traversed a considerable portion of mucous surface. Nor ought it to be forgotten, that cultivation and artificial habits may have blunted the natural susceptibility of our organs, and in some instances changed and depraved their functions: certain qualities for instance are so strongly connected with each other by the chain of association, that by presenting only one to the mind, the other links follow in succession.[89] It has been remarked, that