Most of the crustaceous lichens are merely gray filmy patches inseparable from their growing places, indefinitely spreading, or bounded by a narrow dark border, which always intervenes to separate them when two species closely approximate, and studded all over with black, brown, or red tubercles. The foliaceous species are usually round rosettes of various colors, attached by dense black fibres all over their under-surface, or by a single knot-like root in the centre. Some are dry and membranaceous; while others are gelatinous and pulpy, like aerial sea-weeds left exposed on island rocks by the retiring waves of an extinct ocean. Some are lobed with woolly veins underneath; and others reticulated above, and furnished with little cavities or holes on the under-surface. The higher orders of lichens, though destitute of anything resembling vascular tissue, exhibit considerable complexity of structure. Some are scrubby and tufted, with stem and branches like miniature trees; others bear a strong resemblance to the corallines of our seashores; while a third class, “the green-fringed cup-moss with the scarlet tip,” as Crabble calls it, is exceedingly graceful, growing in clusters beside the black peat moss or underneath the heather tuft, “And, Hebe-like, upholding Its cups with dewy offering to the sun.” As an illustration of the extraordinary appearance which lichens occasionally present, I may describe the Opegrapha, or written lichen, perhaps the most curious and remarkable member of this strange tribe. In her cacti and orchids sportive Nature often displays a ludicrous resemblance to insects, birds, animals, and even the “human face and form divine”; but this is one of the few instances in which she has condescended to imitate in her vegetable productions the written language of man. A cryptogam is in this case a cryptogram! The crust of the curious autograph of nature is a mere white tartareous film of indefinite extent, sometimes bounded by a faint line of black, like a mourning letter. It spreads over the bark of trees, particularly the beech, the hazel, and the ash. On the birch-tree--whose smooth, snow-white vellum-like bark seems designed by nature for the inscription of lovers’ names and magic incantations--it may often be seen covering the whole trunk. The fructification consists of long wavy black lines, sometimes parallel like Runic inscriptions; sometimes arrow-headed, like the cuneiform characters engraved upon the monumental stones of Persepolis and Assyria; and sometimes gathered together in groups and clusters, bearing a strong resemblance to Hebrew, Arabic, or Chinese letters.