174 FIRST FORMS OF VEGETATION. 
Grecian Archipelago, and on the coasts of China 
and Peru. In the Indian collection of raw vege- 
table products exhibited in the Crystal Palace of 
1851, several specimens of orchil from India, Cey- 
lon, and Socotra were shown ; and an explanatory 
note appended to some from the bare, desolate 
Gibraltar of the Red Sea, the rock of Aden in 
Arabia, stated most suggestively— Abundant, 
but unknown as an article of commerce. It is 
probable that it occurs on the maritime rocks of 
all tropical countries in equal profusion. 
In appearance this valuable lichen resembles a 
diminutive leafless shrub, forked, and subdivided 
into numerous roundish, irregular branches. It is 
tough and leathery in texture, of a whitish or blue 
grey colour, and covered with a mealy powder, or 
scattered warty excrescences. It is imported in 
the same state in which it is gathered from the 
volcanic rocks ; and those who prepare it for the 
use of the dyer grind it between stones, so as 
thoroughly to bruise but not to reduce it to pow- 
der, moistening it occasionally with ammonia 
mixed with quick-lime. By this process it ac- 
quires in a few days a purplish-red tinge, and is 
found to form a confused mass of violet-coloured 
threads. In this state it is employed to give the 
English broadcloths that peculiar lustre and purple 
tint, when viewed in a certain light, which are so 
