matically-allied plants is often so great, that to distinguish them specifically requires consideration and careful comparison. The resemblance is more obvious than the difference. There are moreover many plants which are entirely distinct from one another in their inner nature, but which appear strikingly alike if we regard the impression produced immediately on the senses, and the converse of this statement is equally true. Hence the attempt to circumscribe and fix individual forms in the act of describing was at once found to involve difficulties, the solution of which leads directly to the conception of some kind of arrangement. A comparison of the herbals of Fuchs and Bock up to Kaspar Bauhin shows very plainly how these difficulties were gradually overcome, how the describing of single species led necessarily, and without the intention of the describer, to considerations of a distinctly systematic character. Where the species in a group of forms, which we now designate as a genus or family, closely resemble each other in habit, there arose of itself the instinctive feeling that such forms belong to one another. This feeling asserted itself in words when, as was done from the first, a number of such forms were without conscious reflection designated by the same name; thus, to mention one of many examples, we find Bock applying the name Wolfsmilk, Euphorbia, not to one species of the genus, but to several, which he then distinguishes by epithets (common, least, cypress, sweet). The customary mode of expression in the herbals is very instructive on this point; there are, they say, two or more of this or that plant which have not been hitherto distinguished. But this feeling of connection and similarity of kind was produced not only by forms that were closely allied, but also by such as belong to extensive groups of the system; thus the words moss, lichen, fungus, alga, fern, had long served to include a great number of distinct forms, though the separation of these groups had nowhere in truth been carried out with logical precision.
These remarks are important as serving to show in the most
