This accident, however, illustrates another, and a most important point to be remembered, in all arrangements whether of plants, minerals, or animals. No single classification can possibly be perfect, or anything _like_ perfect. It must be, at its best, a ground, or _warp_ of arrangement only, through which, or over which, the cross threads of another,--yes, and of many others,--must be woven in our minds. Thus the almond, though in {202} the form and colour of its flower, and method of its fruit, rightly associated with the roses, yet by the richness and sweetness of its kernel must be held mentally connected with all plants that bear nuts. These assuredly must have something in their structure common, justifying their being gathered into a conceived or conceivable group of 'Nuciferae,' in which the almond, hazel, walnut, cocoa-nut, and such others would be considered as having relationship, at least in their power of secreting a crisp and sweet substance which is not wood, nor bark, nor pulp, nor seed-pabulum reducible to softness by boiling;--but quite separate substance, for which I do not know that there at present exists any botanical name,--of which, hitherto, I find no general account, and can only myself give so much, on reflection, as that it is crisp and close in texture, and always contains some kind of oil or milk. 35. Again, suppose the arrangement of plants could, with respect to their flowers and fruits, be made approximately complete, they must instantly be broken and reformed by comparison of their stems and leaves. The three _creeping_ families of the Charites,--Rosa, Rubra, and Fragaria,--must then be frankly separated from the elastic Persica and knotty Pomum; of which one wild and lovely species, the hawthorn, is no less notable for the massive accumulation of wood in the stubborn stem of it, than the wild rose for her lovely power of wreathing her garlands at pleasure wherever they are {203} fairest, the stem following them and sustaining, where they will.