old tiles, wooden pales, &c. They will most probably be occasioned by the Lichen parietinus, and towards the centre of each specimen the saucerlike bodies to which I allude will be seen, as at (a) Fig. 85.

This species is leaf-like, but many are mere crusts resembling stains of colour. Some species, again, are of considerable size and branched, some resemble coral, some are like stags' horns, others filamentous like hair, and the fructifications of some, as the Lichen pyxidatus (b), resemble drinking glasses; but by examining the fourth volume of Withering, you may learn a great deal on this subject, and if you are lucky enough to have access to the "English Botany" of Sir J. E. Smith, you will find coloured figures of, I believe, about three hundred and fifty British species.

In an economical point of view the Lichens are of more general importance than any other family

deed, of the Laplanders depends on the Lichen rangiferinus, or rein-deer moss, Fig. 83. (c), which forms almost the sole provender of that useful animal. This Lichen is very common on elevated or mountain heaths; but with us it seldom exceeds two or three inches in height, whereas in Lapland its length is above a foot. The rein-deer shows great sagacity in digging it up when covered over with several feet of snow. As this species is very abundant in many parts of Great Britain and Ireland, it might perhaps be found useful in times of scarcity, since a decoction of it in water is said to be very nutritive. Kalm was informed from several sources, that the French who pursue the fur trade in North America, drink its decoction when their provisions run short, during long journeys through the woods. The Iceland moss (Lichen icelandicus) also possesses nutritive properties, as do many others perhaps, which have not yet been submitted to the test of experiment.

The Lichens, however, are chiefly useful as dyestuffs. Litmus is prepared from the Lichen Perellus; and the celebrated Orchal, or Dyer's Lichen (Lichen Roccella), which is used for giving a crimson colour to wool, or silk, is of so much consequence, that it is said to have been sold when little of it was in the market, for one thousand pounds per ton. The Lichen tartareus forms the purple dying-powder, called Cudbear, corrupted from Cuthbert, the name of its inventor. The

Lichen Omphalodes (named Corcar in Ireland) is used by the country people there, and in Scotland, for dying wool of a dull crimson or purple colour. In the Archipelago a lake is prepared from Lichen hispidus; and many other species are used, especially by the inhabitants of mountainous, and rocky districts, for colouring various kinds of wearing apparel.

We shall now attend a little to the sea-weeds, especially the Fuci. Let me suppose that you are rambling on the sea-shore, the tide is at ebb; the waves are murmuring around the rocky points, and breakers which stretch from the land, but all is quiet in the little pools, among the rugged ledges, and loose stones at your feet. You observe various sea-weeds left dry by the recess of the mighty waters, and others waving their tufts of green and crimson in the translucent brine, whose light swell alternately sweeps them to and from the beach. The perriwinkle and dog-whelk are gliding with an almost imperceptible motion over the wave-worn stones; the limpet has formed her vacuum, and adheres strongly to her rocky couch; and the strand-nerite, and the top-shell variegate the sands with studs of grey and saffron. You observe several rocks in the sea at some distance beyond the verge of low water, rising above the surface, and clothed with dark, coarse-looking sea-weeds, as are also many of the stones upon the shore, which have been left dry by the ebbing tide.

To these common and unattractive species we shall now in the first place attend.

you

I have before mentioned the Sargasso, or gulfweed, and the circumstance of its being found floating in immense fields on the surface of the ocean. It is rendered thus buoyant by air vesicles of the size of small peas, which grow in great numbers on its stem, and which were described as berries by the earlier voyagers. Many other Fuci are furnished with air-bladders, though not intended by nature to float entirely detached, like the Sargasso, and will find that some of the common species which grow along our shores are of this description. An apparatus of air-bladders is not, however, entirely confined to sea-plants, since some which grow in fresh water have a similar provision. Of this, the Jussiæa tenella, found in the rivers of Amboyna, is a remarkable example. Along its stalk are many large oval tubercles, full of air, and each of these is compounded of many others, so that the injury which the plant might sustain from foreign bodies striking against it, and breaking the bladders is obviated.* In the frog-bit (Hydrocharis Morsus-ranæ), and a few other British aquatics, something similar may be observed, though, in general, floating leaves preserve their situation by the breadth of their under surface, and the antipathy which their upper has to water, by which the moisture is repelled and thrown off, * Vide Labillardiere's Voyages, vol.i. p. 334.

just as you have seen the drops of rain running like quicksilver over a cabbage-leaf.

The first sea-weed to which we shall attend, is the Fucus nodosus (knobbed fucus), which may be recognised by its compressed forked fronds, and its solitary turgid air-bladders, not supported on pedicles, but in its very substance. See Fig. 86. (a). For a minute description, you must consult Turner's Synopsis of the British Fuci, or the fourth volume of Withering's Arrangement.

The air-bladders in this species are very large, being sometimes, in old plants, even four inches long. They are thick, very tough, and when dried, become as black as ebony; and are sometimes polished and strung into necklaces. The boys, in Scotland, select the largest of these air-bladders, and cutting them transversely at the end, transform them into whistles; on which account the plant is there named "Sea-whistles." The Fucus nodosus is often six or more feet long, and as its air-bladders are not only large, but very numerous, it will be obvious, that, at high water, the strain upon the plant, produced by its buoyancy, and the action of the waves, must be very great. It appears that this, and some other fuci, have no dependance on their root for nourishment, and therefore, instead of being ramified, it is merely a disc or button, by the adhesion of which, assisted perhaps by atmospheric pressure, the weed keeps an uncommonly