170 FIRST FORMS OF VEGETATION. 
time a dreadful scourge in the country, ranging 
the gloomy pine forests in immense herds, com- 
mitting fearful havoc among the sheep-folds and 
cattle-sheds, and when rendered desperate by 
hunger, even attacking travelling parties and the 
houses of the inhabitants. Chemists have detected 
oxalic acid in several species of crustaceous lichens 
growing on the bark of trees, and distinguished by 
an intensely bitter taste ; and in one or two species 
in such abundance, that 100 parts yielded 18 of 
lime, combined with 29'4 of oxalic acid. The ox- 
alate of lime bears the same relation to lichens as 
carbonate of lime to the corals, and phosphate of 
lime to the bony structure of the more highly 
organized animals. On account of this circum- 
stance, some of the crustaceous lichens are exten- 
sively employed in France in the manufacture of 
oxalic acid ; and a small proportion of what is now 
used in this country is derived from this source. 
In London, various species of tree-lichens are sold 
for the use of bird-stuffers, who line the inside of 
their cases, and decorate the miniature trees upon 
which the birds perch, with their shaggy leaves, so 
as to give them a more picturesque and natural 
appearance. The inhabitants of Smoland in 
Sweden are said to scrape a peculiar species of 
yellow crustaceous lichen from old pales, walls, 
and rocks, and mix it with their tallow, to make 
