And on flints in the soil: Lecidea crustulata and Rhizocarpon confervoides. They found that Peltigera spuria colonized very quickly the burnt patches of earth which are of frequent occurrence in Epping Forest, while on wet sandy heaths amongst heather they found associated Cladonia sylvatica f. tenuis and Cl. fimbriata subsp. fibula.

c. On bricks, etc. Closely allied with siliceous soil-lichens are those that form communities on bricks. As these when built into walls are more or less smeared with mortar, a mixture of lime-loving species also arrives. Roof tiles are more free from calcareous matter. Lesdain[1149] noted that on the dunes, though stray bricks were covered by algae, lichens rarely or never seemed to gain a footing.

There are many references in literature to lichens that live on tiles. A fairly representative list is given by Lettau[1150] of “tegulicolous” species.

Several of these are more or less calcicolous and others are wanderers, indifferent to the substratum. Though certain species form communities on bricks, tiles, etc., none of them is restricted to such artificial substrata.

d. On humus. Lichens are never found on loose humus, but rocks or stumps of trees covered with a thin layer of earth and humus are a favourite habitat, especially of Cladoniae. One such “formation” is given by Bruce Fink[1151] from N. Minnesota; with the exception of Cladonia cristatella, the species are British as well as American:

e. On peaty soil. Peat is generally found in most abundance in northern and upland regions, and is characteristic of mountain and moorland, though there are great moss-lands, barely above sea-level, even in our own country. Such soil is of an acid nature and attracts a special type of plant life. The lichens form no inconsiderable part of the flora, the most frequent species being members of the Cladoniaceae.

The principal crustaceous species on bare peaty soil in the British Isles are Lecidea uliginosa and L. granulosa. The former is not easily distinguishable from the soil as both thallus and apothecia are brownish black. The latter, which is often associated with it, has a lighter coloured thallus and apothecia that change from brick-red to dark brown or black; Wheldon and Wilson[1152] remarked that after the burning of the heath it was the first vegetation to appear and covered large spaces with its grey thallus. Another peat species is Icmadophila ericetorum, but it prefers damper localities than the two Lecideae.