106 EXPLOITATION OF PLANTS 
quantities for this purpose. The collectors obtained 
from rd. to 2d. per |b. for the lichen, and could gather 
from 20-30 lb. in a day. As the cost of transport of 
the bulky lichens from remote districts is heavy, it 
would be more efficient for the collectors themselves 
to develop and extract the dyes and export them in the 
more convenient powder form. 
The other lichen dyes can be extracted with boiling 
water. They give shades of brown and yellow of great 
permanence. They are still used in the Highlands, 
where they are known as “‘ crottles,’”” or crotal, and in 
the West of Ireland. Parmelia saxatalis and P. ompha- 
loides, collected and dried in July and August, are used 
to dye woollens for tweeds; the peculiar smell of 
Harris tweed is partly due to the use of these lichens. 
Ramalina scopulorum also gives a fine yellow brown, and 
several other Parmelia species give similar colours. 
The dyeing process is very simple. The dried 
*crottle ’” and cloth are laid in alternate layers until 
the bath is full, cold water is added, the whole is brought 
to the boil, and boiled till the colour is strong enough. 
Alum is sometimes used to mordant the cloth, but it 
does not seem to be necessary (see Mairet, 1916, chap. 
on “‘ Lichen Dyes,” also Lindsay, 1855). If the dyeing 
principle of crotal could be extracted and put up in 
portable form it might prove a useful commercial 
product, as the demand for fast brown shades for cloth 
is likely to be permanent. 
Indigo.—Although direct dyes are simple in applica- 
tion, they are usually (with the striking exception of 
crotal) rather fugitive, and consequently of limited 
applicability. The most permanent kind of dye is one 
