resembles the frond of many chlorospermous seaweeds, and here the chlorophyll, which in most Lichens is confined to the gonidia, is diffused through, or dissolved in, the thalline mucilage. Other Collemas have a thallus of a leathery or cartilaginous consistence, more resembling the normal or typical Lichen-thallus in structure. In some species the thallus is naked; in others, granulose or furfuraceous; and in a few, papulose or marked on the surface by pellucid papules or vesicles, which Scherer regards as in some way subserving, like the gonidia, the function of reproduction. The apothecium is usually developed in a thalline wart, and is at first globose, becoming gradually expanded, open, and discoid. In species having a thick and dense thallus it is generally scutellate, having a distinct thalline exciple; but in other cases this exciple is very thin, pellucid, evanescent, or it is covered by the thalamium, which becomes flattened and then convex (patellæform). In a few a proper exciple has been described, in which case the apothecium is patellate.

* Thallus filamentous; apothecia patellaform.

1. COLLEMA PUBESCENS (pubesco, to become mossy or downy). Thallus black, decumbent. Filaments capillaceous, terete-elongate, somewhat simple, entangled or loosely inter

woven, softish. Apothecium black,—at first immersed in fusiform or ovoid, sub-apical swellings of the thalline filaments, and resembling in structure the apothecium of Lichina. (E. B. 2318.)

Not uncommon on alpine rocks on many of our Highland mountains, growing frequently along with varieties tristis and lanata of Parmelia Fahlunensis, with which it was classed by older writers in the genus Cornicularia. It is often found in small cavities in the rock which are occasionally filled with rain-water. The synonymy of this species has varied much, and it has long sought a resting-place in classification. Several authors have claimed it as an Alga; while according to others it has been by turns the Lichen pubescens, Cornicularia pubescens, Ephebe pubescens, and Collema pubescens. The thecæ are clavate; the spores elliptic, hyaline, and bilocular. The latter resemble, in their development, the spores of the genus Lichina. Its spermogones are to be looked for in minute spheroidal swellings towards the apex of the thalline filaments. The sterigmata are minute, simple, linear, and closely aggregated; the spermatia acrogenous, oblong, with truncate extremities. Bornet describes spermogones as occurring on one plant, and apothecia on another; if this be uniformly the case, it must be

regarded as a diœcious species.* Indeed in the speculative but laborious dissertation of Bayrhoffer (Einiges über Lichenen und deren Befruchtung,' Berne, 1851) Lichens are described as normally monoecious and diœcious. **Thallus foliaceous, when dry membranaceous, when moist flaccid; apothecia patellaform and scutellate.

2. COLLEMA ATRO-CÆRULEUM. Thallus very thin and somewhat diaphanous, lacerate-laciniate, reticulate-lacunose, from lead-coloured becoming reddish, when moist olivecoloured. Apothecia patellaform, minute, superficial, pale brown. The lacinia vary in size, being sometimes narrow and imbricately arranged; in the most common variety, var. lacerum, they are broadish, sinuate, with dentate-ciliate margins.

Creeping over moss, and also growing sometimes on trees, rocks, and the ground in various Highland districts. This is one of the species possessing a distinct cortical layer, composed of intimately united, polyhedral cellules, while the medullary tissue resembles the filamentous texture of the

* For minute anatomy and synonymy, vide Bornet, 'Annales des Sciences Naturelles,' vol. xviii. 1852, p. 155: Berkeley, in Annals of Nat. Hist. 1851 Flotow, Bot. Zeitung, 1850, and 'Linnæa,' 1850: Davies, on L. scaber and some of its allies, in Trans. Linn. Soc. London, 1815.