In the subdivision of a genus there is often a remarkable difference in the properties of the species; there are, for instance, _Solanums_, _Lettuces_, _Cucumbers_, and _Mushrooms_, both esculent and poisonous. The _Digitalis_ or _Foxglove_, and the _Verbascum_, or common _Mullein_ of our fields, are included in the same Natural family, and yet the one is as active, as the other is mild in its effects; the plants of the natural family of _Contortæ_ abound with a highly acrid milky juice, but Dr. Afzelius met with a shrub of this order at Sierra Leone, the milk of whose fruit was so sweet, as well as copious, as to be used instead of cream for tea; this is certainly what no one could have guessed from analogy. The same individual will vary from culture or other circumstances, as much as any two plants which have no botanic affinity; the Chamomile, _Anthemis Nobilis_, with which we are well acquainted, may have its whole disk changed by cultivation, to ligulate white florets, destitute of medicinal properties. But, what is more embarrassing, the different parts of the same plant have often very different powers; a fact which is beautifully exemplified in the _Podophyllum Peltatum_, or May Apple, the _leaves_ of which are poisonous, the root powerfully cathartic, and the _fruit_ agreeably esculent; so the leaves of the _Jatropa Manihot_ are employed as a common esculent, while its root secretes a most virulent poison; but we need not seek further for an example than the fruit of the Lemon, the juice of which is _acid_, its seeds _bitter_, and its _rind aromatic_; in some instances it happens that the energy of a plant is concentrated in one particular part, and that all the rest is absolutely inert; thus, the root of the _Convolvulus Scammonia_, is the only portion of that plant which possesses any medicinal quality;[86] and the tree which yields the drastic _Camboge_, presents at the same time an esculent fruit, which is eaten by the natives with as much impunity as the orange; yet, notwithstanding all these difficulties, botany is capable of furnishing us with analogies which will lead to important conclusions with respect to the medicinal properties of different vegetables. The system of Linnæus, although in a great degree artificial, corresponds in a surprising manner with the natural properties of plants; thus a plant whose _calyx_ is a double valved _glume_, with three _stamina_, two _pistils_, and one _naked seed_, bears seeds of a farinaceous and nutritious quality; a flower with twelve, or more _stamina_, all of which are inserted in the internal side of the _calyx_, will furnish a wholesome fruit; whereas a plant whose flower has five _stamina_, one _pistil_, one _petal_, and whose fruit is of the _berry_ kind, may at once be pronounced as poisonous.