GENERAL CHARACTERS OF MOSSES. 31 and brought to perfection, in this obscure part of the world, a thing which appears of so small importance, look with unconcern upon the situation and sufferings of creatures formed after his own image? Surely not.-Reflections like these would not allow me to despair. I started up; and disregarding both hunger and fatigue, travelled forwards, assured that relief was at hand, and I was not disappointed." 29. Mosses are found in all parts of the world in which the atmosphere is moist; but they are far more abundant in temperate climates than in any between the tropics. They are among the first vegetables that clothe the soil with verdure in newly-formed countries; and they are the last that disappear when the atmosphere ceases to be capable of nourishing vegetation. The first green crust upon the cinders with which the surface of Ascension Island was covered, consisted of minute Mosses. This tribe forms more than a fourth of the whole vegetation of Melville Island, one of the most northerly spots in which any plants have been observed; and the black and lifeless soil of New South Shetland, one of the islands nearest to the South Pole, is covered with specks of Mosses struggling for existence. 30. Besides their power of resisting extremes of temperature, Mosses exhibit a remarkable tenacity of life, when their growth is checked by the absence of moisture; so that they may often be restored to active life, even when they have been dried for many years. Hence they offer abundant sources of interest to the observer of Nature, at a season when vegetation of other kinds is almost entirely checked. For it is most curious to observe how gay these little Mosses are on every wall-top during the winter months, and in the early spring,-almost, or perhaps the only things which seem to enjoy the clouds and storms of the season. They choose the most exposed situations, spread out their leaves, and push up their delicate urns, amidst rain, frost, and snow, and yet there is nothing in their simple and tender structure from which we could infer their capability of resisting influences so generally destructive to vegetation. But it is with Plants as with 32 MOSSES.-LIVERWORTS. Animals. The more simple and lowly the being, the greater is usually its tenacity of life under circumstances which depress the vital powers of higher kinds; whilst the influences which they require are often too powerful for it. Thus, Mosses and Lichens, overstimulated by heat and dryness, wither away in summer; but vegetate freely at a season when there is no other vegetation, and when their humble fabrics cannot be overshadowed by a ranker growth. 31. Mosses were fancifully termed by Linnæus, servi, servants or workmen; for they seem to labour to produce vegetation in newly-formed countries, where soil can scarcely yet be said to be. This is not their only use, however. They fill up and consolidate bogs, and form rich vegetable mould for the growth of larger plants, which they also protect from cold during the winter. They likewise clothe the sides of lofty hills and mountain-ranges; and powerfully attract and condense the watery vapours floating in the atmosphere, and thus become the living fountains of many streams. They are sometimes so completely dried up by drought, that they escape notice; and then, when moistened by rain, they appear to have suddenly clothed a barren heath or overspread a dry wall with verdure, on which, however, they really existed before. 32. Closely connected with the Mosses is the tribe of Liverworts, the lower forms of which are nearly connected with the Lichens. Some of them differ but little in their general characters from Mosses, being distinguished by certain peculiarities of fructification. Others, however, have no distinct stem or separate leaves; but extend horizontally into a flat leaf-like expansion; the fructification is sometimes elevated above this on a little stalk; but in the tribes most nearly allied to the Lichens, it is imbedded in it, as it is in that group. Their general habits closely resemble those of the Mosses. Their leafy expansions are soft and green; differing much, therefore, from the dry scaly crusts of the Lichens. They are capable of reviving, like the Mosses, after being dried up; and, from the rapidity of their growth, and a peculiarity in LIVERWORTS.-MARCHANTIA. 33 their mode of propagation, they are often seen to spread over a damp surface with great rapidity. One of the most common species is the Marchantia polymorpha, which will be often referred to in this treatise, on account of the many interesting facts which the attentive study of it has disclosed. It is usually found growing on moist surfaces, and often where there is little or no soil; it is very common in the chinks between paving-stones in unfrequented places, and on the surface of the earth contained in garden-pots, as also upon walls which from any cause are kept constantly damp. Fig. 4. Marchantia polymorpha, one of the commonest of the Liverworts. 33. Besides the regular fructification, this little plant has a very curious apparatus for the production of small leafy bodies, which may be regarded as buds, and which spontaneously separate from the parent structure and develope themselves into new beings. As these, when mature, are liable to be washed out of their receptacle by rain, and to be carried to different parts of the neighbouring surface, and as they grow very rapidly whilst supplied with moisture, the rapid extension of the plant under such circumstances is easily accounted for. The little receptacles, of a basket form, in which these are produced, may be generally seen in some stage of their growth on the upper side of the leafy expansion of which the plant consists; and they constitute beautiful objects for a low magnifying power of the microscope. The budlike bodies, having the form of flat disks like coins, may often be seen to grow whilst still contained in their receptacle, and even to unite themselves, as it were, with the parent plant. 34. The group of Cryptogamic plants termed Lichens are mostly dry, hard, scaly crusts, destitute of leaves and stems, and even of any thing bearing a resemblance to them; they grow upon bare walls, the trunks of old trees, and other such situations, in which they are much exposed to light, and not abundantly sup plied with moisture. In their general structure they nearly D 34 GENERAL CHARACTERS OF LICHENS. approach to the Sea-weeds; and differ from them chiefly in being adapted to live in air instead of in water. The dry hard crust is Fig. 5. Parmelia perforata, usually of a greyish colour; its upper Lichen with projecting shields. 35. There can be no doubt that the greater part of this tribe derive their nourishment from the atmosphere and its contained moisture alone; flourishing as they do upon sterile rocks, without a particle of soil or mould in their neighbourhood. There are many species which ordinarily grow upon the trunks of trees; and these are commonly spoken of as Mosses,-but incorrectly so. The shaggy appearance of the apple-trees of an old Orchard is in general entirely due to Lichens, although a few Mosses may sometimes be found among these. Of such Lichens, by far the greater part vegetate indifferently on all kinds of trees, and they flourish equally well upon a damp wall; so that there is no reason to suppose that they derive any more nutriment from the stems on which they grow, than is afforded by the moisture covering their surface. There is no doubt, however, that some trees are much more favourable to their growth than others. Thus, the Beech, Elm, Sycamore, and Lime, are comparatively seldom found infested with the common Beard-moss, which clothes so profusely the Fir, Ash, Oak, or Birch; so that the MODE OF GROWTH OF LICHENS. 35 poet's epithet of "rude and moss-grown beech" is by no means appropriate. 36. The fructification of the Lichens is not much raised above the general surface, but is usually imbedded in certain parts of it, somewhat differently formed from the rest, and termed shields. The early growth of these plants is favoured by darkness; but for the ripening of the reproductive bodies a considerable quantity of light is required. The development of the shields, which takes place under its influence, is frequently accompanied by so great a change in the general appearance of the plant, that the same species growing in dark and moist places, in which the fructification was not evolved, has been considered to belong to a distinct kind from the perfect specimen. No true Lichens are ever found in mines, caverns, or other places deprived of light; nor are there any that grow entirely under water, although some species, which connect this group with the Sea-Weeds, grow on the seashore, where they are alternately submersed and left dry by the tide. 37. To the Lichens may well be applied the title of Vernaculi, or bond-slaves, which Linnæus fancifully gave to the Sea-Weeds; regarding them as fettered to the rocks on which they grow. For the Lichens seem as it were chained to the soil which they labour to improve for the benefit of others, although they derive no nourishment from it themselves. The mode in which they prepare the sterile rock for the reception of plants which require a higher kind of nourishment, is most remarkable. They may be said to dig for themselves graves, for the reception of their remains, when death and decay would otherwise speedily dissipate them. For whilst living, these Lichens form a considerable quantity of oxalic acid, (which is a peculiar compound of carbon and oxygen, two ingredients supplied by the atmosphere;) and this acts chemically upon the rock, (especially if of limestone,) forming a hollow which retains the particles of the structure, when their term of connected existence has expired. The moisture which is caught in these hollows finds its way into the cracks and crevices of the rocks; and, when frozen, rends them by its |