Kerner’s opening words on this _symbiosis_ are worth quoting: “In describing the vegetation of a limited area, botanical writers are apt to designate the various species of plants as ‘denizens’ of the country in question. The conditions under which the plants live are likened to political institutions, and the relations existing amongst the plants themselves are compared to the life and strife of human society.” He goes on to speak of the interdependence upon one another of these plants living in the same community; he shows how necessary they are to one another; how they sometimes fight for food, light and air; how some are preyed upon and oppressed by others, “and how not infrequently quite different species join together in order to attain some mutual advantage.” And so he comes to the curious history of the lichens. Some forty or fifty years ago there arose a furious battle around the lichens, humble little creatures enough, plastered on almost every rock and stone and tree in creation. During the ’sixties of the last century Schwendener, a Swiss botanist—professor successively at Basle, Tübingen and Berlin—wrote a number of papers in scientific publications, in which he proved to his own satisfaction that lichens are not individual plants, but compound existences consisting of an alga and a fungus. His investigations were followed up by one Bornet, and he had a numerous following largely attracted by the charm of novelty and the ingenuity of invention. Kerner went so far as to say that “the continued study of lichens has tended only to secure for the Schwendenerian theory a more wide and universal recognition.” Dr. Cook, however, the great authority on cryptogamic botany, laughs at this mystic union as a “fairy tale.” He treats it with the same contempt that St. Paul, in his letter to Titus, expressed for “Jewish fables.” He says: “The high priest Schwendener thus expressed his dream: ‘As the result of my researches, all these growths (lichens) are not simple plants, not individuals in the ordinary sense of the word; they are rather colonies, which consist of hundreds and thousands of individuals, of which, however, one alone plays the master, whilst the rest, in perpetual captivity, prepare the nutriment for themselves and their master. This master is a fungus of the class ascomyceter, a parasite which is accustomed to live upon others’ work; its slaves are green algæ, which it has sought out, or, indeed, caught hold of, and compelled into its service. It surrounds them, as a spider its prey, with a fibrous net of narrow meshes, which is gradually converted into an impenetrable covering; but whilst the spider sucks its prey and leaves it dead, the fungus incites the algæ found in its net to more rapid activity—nay, to more vigorous increase.’”