An industry on Dartmoor that has become completely extinct is the collection of lichen from the rocks for the use of the dyers. There exists in MS. an interesting book by a Dr. Tripe, of Ashburton, recording what he saw and did each day, at the close of last century. He says that he observed women scraping off the lichen from the rocks near the Drewsteignton cromlech. This they sold to the dyers, who dried it, reduced it to powder, and treated it with a solution of tin in _aqua fortis_ and another ingredient, when a most vivid scarlet dye was produced. The lichen is called botanically _Lichinoides saxatile_. Other lichens were employed to give purple and yellow colours. The cudbear and crab's-eye lichens (_Lecanora tartarea_ and _Lecanora parella_) gave a dye of a royal purple, and the two species called _Parmelia saxatilis_ and _Parmelia omphalodes_ gave a yellowish brown. Moss also was employed for the purpose; the _Hypnum cupressiforme_ yielded a rich reddish brown.
"Lichens and mosses," says Mr. Parfitt, "are the pioneers of the vegetable kingdom in attacking the hard and almost impenetrable rocks, and so preparing the way for the more noble plants--the trees and shrubs--by gradual disintegration, and by adding their own dead bodies to the soil, enrich it for the food of others."[25]
It is marvellous to see how the lichen attaches itself to the granite. A harshly glaring piece that the quarrymen have cut is touched with fine specks that spread into black and crocus-yellow circles, and tone down the stone to a sober tint. Unhappily of late years there has been much firing of the furze and heather on the moor, and the flames destroy the beautiful lichens and mosses, and leave the old stones white and ghostly, not to be reclothed with the old tints for centuries.
I do not think that we have any idea of the slowness with which the lichens spread; a century to them is nothing--it passes as a watch in the night. There is a granite post I often go by. It was set up just seventy years ago, and on it the largest golden circle of the _Physcia parietina_ has attained the diameter of an inch. Mr. Parfitt mentions in connection with it a rocky crag at Baggy Point, North Devon, where it covers the whole surface with a coat of golden colour. It spreads more rapidly on slate than it does on granite, and especially on such slates as are liable to rapid disintegration. The Woodland and the Coryton slates are readily attacked by it. The growth begins with a splash about the size of a sixpence, and increases to that of a plate, when the centre breaks up, and the ring becomes detached in fragments which meet others, and so appear to cover the rock or roof.