172 FIRST FORMS OF VEGETATION. 
own leaves; but strange to say, these are the least 
valuable species to the dyer. The lichens which 
are richest in colorific principles are crustaceous 
species growing on rocks, and utterly destitute of 
Fic. 15.—ROCCELLA TINCTORIA. 
colour in their natural state ; and it is one of the 
most striking triumphs of chemistry as applied to 
the arts and manufactures, that by its means some 
of the finest shades of red, purple, and yellow are 
extracted from such unlikely substances. The 
lichen popularly known as Orchil (Fig. 15) affords 
a remarkable illustration of the extent to which 
colorific principles are developed in these out- 
wardly hueless plants. It derives its generic name 
Roccella from a Florentine family called Rucellai, 
whose founder, for a long time a trader in the 
Levant, discovered in the sixteenth century the 
art of preparing a most valuable dye from it, by 
