Uses. On account of the cell-wall being composed of Lichenstarch (Lichenin), the Iceland-Lichen and Manna-Lichen (Lecanora esculenta) are used as food; the latter grows on stones, in the deserts of Asia and North Africa, and is often torn loose in large masses and carried away by the wind. The Reindeer-Lichen is not only the principal food of the reindeer, but it is also used in the manufacture of Danish brandy. Cetraria islandica (Lichen islandicus) is OFFICINAL. Colouring materials (lacmus, orseille, persio) are made from several species, especially from Roccella tinctoria (from the rocky coasts of the Mediterranean). Parmelia saxatilis and particularly Lecanora tartarea are used for colouring purposes in the Northern countries.
About 2,000 species of Lichens have been described. If we disregard the Basidiolichenes, which will be considered on page [176], the remaining Lichens (Ascolichenes) may be divided into the two following orders according to the structure of the fruit-bodies:—
Order 1. Pyrenolichenes. The ascocarps (apothecia) are spherical or flask-shaped, as in the Pyrenomycetes, more rarely linear (Graphis).
According to the nature of the thallus, these Lichens may be divided into:—
a. Thallus homoiomerous, but not gelatinous, branching according to the mode of growth of the Algæ: Ephebe (Fig. [133]), with Algæ of the genus Stigonema.
b. Thallus homoiomerous, gelatinous: Lichina.
c. Thallus heteromerous, crustaceous: Verrucaria, Pyrenula; Graphis (Fig. [139]), which may be considered as Hysteriaceæ with gonidia; several species of Graphis are common on bark.
d. Thallus heteromerous, foliaceous: Endocarpon.
e. Thallus heteromerous, fruticose: Sphærophorus.
Order 2. Discolichenes. These, as in the Discomycetes, have open apothecia, which, as a rule, are cupular, more rarely hemispherical (Cladonia).