129 WAYSIDE AND WOODLAND BLOSSOMS. 



The other species figured in our plate, the Wall-lichen 

 (Physcia parietina], is also very common, forming the familiar 

 orange stains upon walls and maritime rocks. A closely 

 allied species, the grey Parmelia saxatilis^ is common on tree- 

 trunks : it has been used time out of mind in the production of 

 a brownish-red dye for wools. Several others of the same 

 genus are valuable in a similar direction : our own Parmelia 

 perlata, which grows on tree trunks, is largely imported from 

 the Canaries as a dye-weed, and has been sold at as high a 

 rate as ,200 per ton. 



Lichens are generally of slow growth and long life. Mr. 

 Berkeley kept watch upon a patch of Lecidia geographica for 

 twenty-five years, and found little change in it all that time. 

 The Rev. Hugh Macmillan recounts how he found on the top 

 of Schiehallion a species of lichen encrusting quartz rocks, 

 which exhibited beneath the lichen the marks of glacial action 

 as distinct and unchanged by atmospheric effects as though the 

 glacier had only passed over them yesterday. He suggests 

 that the lichen may reckon its days back very nearly if not 

 quite to the glacial period in Britain ! 



There are upwards of a thousand British species, and the best 

 list of them will be found in " Crombie's British Museum Cata- 

 logue of Lichens," of which the first part was published in 1 894. 



Mosses (Musci). Plate 127. 



Another important tribe of flowerless plants, to which we 

 must be content with merely giving the general characters, for 

 in a volume primarily intended as a guide to wild-flowers we 

 must not occupy too much space with plants that do not 

 produce flowers. At the same time, we believe the non- 

 botanical among our readers will be glad to have a slight 

 introduction, upon the strength of which they may cultivate the 

 closer acquaintance of a most beautiful and interesting group 

 of plants. 



