1903-1904-] -^ Short Talk on Lichens. 93 



the British Islands ' is very dry and puzzling reading. The 

 species of Cladina are more easily determined. They have 

 no leafy thallus, the podetium has no scyphi, they are re- 

 peatedly branched, are more or less smooth, the apothecium 

 terminal, and some have the axils perforated. 



The species of the genus Cladonia are for the most part 

 very variable, and are so connected by intermediate states 

 and forms (the result very likely, in part at least, of 

 hybridism) that it is difficult to separate them. The conse- 

 quence is, that no two lichenologists agree as to species or 

 varieties. To add to the difficulty, the chemical reactions of 

 the thallus, apart from the character of the basal thallus and 

 the podetia, are not of decided value in this genus. On this 

 point Dr Nylander says, " The genus Cladonia is not so well 

 adapted to show the excellence of reactions on account of the 

 tinctorial particles being often but sparingly present by reason 

 of the frequent tenuity of the cortex." 



Cladoniae are distributed all over the world, and our own 

 British Islands are particularly rich in species, though, strange 

 to say, the true Cladina rangiferina is as much absent from 

 Ireland as reptiles are. Cladonise are chiefly terricole species, 

 preferring peaty soils, and as a rule open and exposed habitats, 

 and some grow on semi-putrid wood. They are very social in 

 their habits. In northern regions lichens form by far the 

 largest portion of the vegetation. Here Cladonise, mixed with 

 other lichens as Stereocaulon, are seen spreading over extensive 

 tracts almost to the entire exclusion of other vegetation. It 

 is a beautiful sight to see an almost limitless plain in Lapland 

 and similar countries covered with Cladina rangiferina a foot 

 high, giving the appearance of snow tinted with various colours 

 from the admixture of other lichens. 



The most useful and interesting of all the Cladonise is 

 undoubtedly Cladina rangiferina and its allied species C. 

 sylvatica, which latter is by far the more common. In Norway 

 it occurs in three varieties, sylvatica, alpestris, and granclis. 

 The true C. rangiferina is rather rare in the British Islands, 

 though perhaps the most widely distributed of all lichens. 

 It is not often found in fruit. It is called reindeer moss, 

 cow moss, white moss, and caribou moss. It is invalu- 

 able to the inhabitants of northern latitudes. It is on a 



