LICHENS. 153 
excursions generally took place once every three 
years, for the lichen required that time to arrive at 
maturity, after the spots where it flourished had 
been cleared. Olafsen and Povelsen, in their in- 
teresting Travels in Iceland, observe that a family 
could collect four tons in a week during the 
season, with which, they say, they were better off 
than with one ton of wheat. We are also informed, 
in .a report on this lichen, published several years 
ago by the Saxon Government, that the meal 
obtained from it, when mixed with wheat-flour, 
produces a greater quantity of bread, though 
perhaps of a less nutritious quality, than could be 
manufactured from the latter alone. Of gluten or 
nitrogenous flesh-forming material, it contains only 
one per cent.; but it contains no less than forty- 
seven per cent. of lichenine, which is a form of 
starch ; with three per cent. of sugar, and ten of gum 
and extractive. Its usefulness as an article of diet 
or of the Materia Medica must thus depend chiefly 
upon its lichenine or starch. The extremely bitter 
taste, however, by which it is characterized,—owing 
to a peculiar astringent principle in it called cetra- 
rine which has been procured in a state of purity, 
in the form of a white powder like magnesia, by 
Herberger,—has always proved a great drawback 
to its adoption as an independent article of food, 
especially in this country. In Iceland and Lap- 
