LICHEN COMMUNITIES 369 



On bare heaths of gravelly soil in Epping Forest Paulson and Thompson^ 

 describe an association of such lichens as : 



Baeomyces roseus. Cladonia iiKicilenta. 



Baeomyces rufiis. Cladonia furcata. 



Pycnothelia papillaria. Cetraria aculeata. 



Cladonia cocci/era. Peltigera spicria. 

 Lecidea granulosa. 



And on flints in the soil : Lecidea criistidata and Rhizocarpon confer- 

 voides. 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 syl- 

 vatica f tennis and CI. fimbriata subsp. fibitla. 



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- 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^ of" tegulicolous " species. 



Verrucaria nigrescens. Placodiiiiii elegans. 



Lecidea coarctata. Placodiu7n imcroriim. 



Candelariella vitellina. Xanthoria parietina. 



Lecanora dispersa. Khizocarpon alboatricm var. 



Lecanora galactina. Buellia myriocarpa. 



Lecanora Hageni. Lecidea demissa. 



Lecanora saxicola. Physcia ascendens. 



Parmelia cotzspersa. Physcia caesia. 



Placodium teicholytum. Physcia obscura. 



Placodiiim pyraceum. Physcia sciastrella. 

 Placodium decipiens. 



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^ from N. Minnesota ; with the exception of Cladonia cristatella, the 

 species are British as well as American : 



Cladonia furcata. Cladonia rangiferina. 



Cladonia crisiatella. Cladonia uncialis. 



Cladonia gracilis. Cladonia alpestris. 



Cladonia verticillata. Cladonia turgida. 



' Paulson and Thompson 1913. ^ Lesdain 1910-. ^ Lettaii 1911, * Fink 1903. 



S. L. 24 



