248 PLANT LIFE. 



resembling rosettes of black paper, or leaden-grey discs 

 with black fringes at the edge. It is one of the hardiest 

 genera, and lives in the most exposed situations and in 

 a very variable climate. 



The Crustaceous Lichens produce crusts or scaly 

 matter or stains on rocks, stones, wood, or bark. They 

 are exceedingly difficult to study especially as they 

 adhere by the whole under surface so that it is necessary 

 to break off pieces of the stone or wood to obtain 

 specimens. Lecidea alone consists (according to 

 Leighton), of 393 British species, of which no less than 

 230 grow on rock or stone. Even this is a large 

 number, though it is insufficient for other botanists who 

 have raised the number of species to six or seven 

 hundred. An old rock or stone wall seems at first to 

 be of a monotonous indeterminate colour, probably 

 some sort of dull grey, in no way attractive ; yet, if 

 such a surface is closely examined, the variety of ex- 

 ceedingly delicate colour-contrasts in these crust and 

 stain lichens is seen to be very great. These Lecanoras 

 and Lecideas vary both in the colour of the crust, and in 

 that of the tiny cups, which are always different in tint, 

 though in harmony with the ground colour of the 

 lichen. Shades and contrasts are to be found amongst 

 them, which appear nowhere else in Nature, and are 

 certainly never copied by artists. The colour of the 

 body or crust is found to vary, being bright yellow, 

 pale ochre, citron yellow, chestnut colour, mouse colour, 

 different shades of grey and green, cream colour, lead 

 colour, blue-black or pure black, tawny, brown, rusty 

 red or pure white. The cups in Lecidea are generally 

 black and without a distinct rim. They are distinguished 

 by this last character from those of Lecanora which 

 have a very marked border, and a rim distinct from the 



