the gelatinous substance lichenin, and the "reindeer moss" (Cladonia rangiferina), which grows abundantly in the Arctic regions, and forms the chief nourishment of the reindeer. Other lichens are valuable for medicinal purposes, as Parmelia parietina, used as a remedy for fever. Several other lichens such as "Roccella tinctoria" are employed in dyeing important shades of crimson and purple in silk and wool. This colouring matter, known as arehil, or orchil, is obtained from various lichens natives of the rocks of the Canary and the Cape de Verd Islands, and is principally used in conjunction with aniline dyes to improve their tints. The Parmelia esculenta of Asia Minor and the Sahara is identified by some with the "Manna" of Scripture.
In the vicinity of lichens, the Musci, or mosses, are generally to be found. Like the lichens, wherever vegetation can be sustained they are present, affording protection to the roots and seeds of more highly organized plants, and by their spongy texture retaining moisture which preserves other plants from the drought of summer. Mosses abound in our pastures and woods, attaching themselves both to the living and dead trunks and branches of trees. They also grow luxuriously in marshy places, and become a medium for the conversion of these into fruitful fields. The bog-mosses (Sphagnaceæ) grow in water or on some solid sub-stratum, and contribute largely to the formation of peats.
When nature has provided a soil, her next care is to perfect the growth of her seeds and then to disperse them. This is effected by the structure and arrangement of the seed varying according to the nature of its particular habitat. When the seed, or mature ovule, is ripe, it bursts the capsule in which it is contained and falls to the ground, or is scattered by the wind. Some seeds, as the Cuckoo-flower (Cardamine pratensis), escape by an elastic jerk at the moment of their explosion, and by this means are cast to a distance. Others like those of the maple, elm, and ash have wing-like appendages which enable the seed to be curried in the air; others again, like the thistle and dandelion, are provided with downy hairy filaments, by means of which they are conveyed long distances by the breezes.
Birds, quadrupeds and insects are likewise the means of dispersing the seeds of plants, and placing them in situations where they ultimately grow. Amongst the latter is the squirrel, which is an extensive planter of oaks. It is related that a gentleman was walking one day in some woods belonging to the Duke of Beaufort, near Troy House, in Monmouthshire, when his attention was arrested by a squirrel, sitting very composedly upon the ground. He stopped to observe its movements. In short time the little animal suddenly quitted its position, and darted to the top of the tree beneath which it had been sitting. In an instant it returned with an acorn in its mouth, and with its paws began to burrow in the earth. After digging a small hole, it deposited in it an acorn, which it hastily covered, and then darted up the tree again. In a moment it was down with another which it buried in the same