Swine are fond of the roots of fern, and will feed freely upon them. We are even informed that, with the inhabitants of Palma, one of the Canary islands, they are sometimes made to supply the place of bread.
It is deserving of remark that, when the root of the fern is cut obliquely across, it presents a kind of figure of the Imperial or Russian eagle; from which circumstance Linnæus was induced to name it Pteris aquilina, or "Eagle brake."
281. The LICHENS constitute a very numerous family of plants, which grow on the bark of trees, on rocks, stones, and other substances; and have an indistinct fructification, in scattered wart-like tubercles, or excrescences, and smooth saucers or shields, in which the seeds are imbedded.
Some of them have a powdery appearance, and others are crustaceous, leaf-like, shrub-like, herbaceous, or gelatinous.
282. The CALCAREOUS LICHEN (Lichen calcareus) consists of a white crust with black tubercles.
This plant, which is found on lime-stone rocks in Wales, and the north of England, is used in dyeing woollen and other cloths a scarlet colour.
283. CRAB'S-EYE LICHEN (Lichen parellus) is a crustaceous, whitish, and granulated vegetable substance, with cups of the same colour, which have a thick and blunt border.
From this lichen, which is found on rocks and stones in mountainous countries, and sometimes on stones near the sea-shore, is prepared the bluish pigment called litmus. It is chiefly collected from rocks in the north of England, packed in casks, and sent to London for sale.
284. TARTAREOUS LICHEN (Lichen tartareus) is a whitish, crustaceous, vegetable production, with yellow cups or shields, which have a whitish border.
The inhabitants of the Highlands of Scotland gather this species of lichen from the rocks, and, after cleaning, and some further preparation, which is kept a secret by the manufacturers, they form it into cakes. These, when dried, are pulverized, and sold to dyers by the name of cudbear, which is a corruption of Cuthbert, the name of its inventor. In conjunction with alum, the powder of the tartareous lichen is used in dyeing scarlet, and also for striking a purple dye; but the colour produced by it is not very permanent.