The tribe of Schistostegei consists of but a single most elegant species. It inhabits shady caverns, which are sometimes lighted by a golden gleam from the refractions of the confervoid shoots of its mycelium-like pro-embryo, which is perennial, and produces a new crop year after year. The urn is subglobose without a peristome, and when young the spore cells radiate from the columella as in the Splachna. The leaves show various intermediate stages between a vertical and horizontal insertion, and are sometimes perfectly free, while at other times they are united. This moss is scarce, and confined to the northern hemisphere.
There are various genera of aquatic mosses in the different tribes, most of them floating plants. Of these are the pleurocarpous Fontinalei, which inhabit the northern hemisphere; their urn, with its double peristome of sixteen teeth, forms a beautiful microscopic object, on account of the latticed work in the inner row, and the cross bars on the outer teeth, which are united at their tips by two and two. The common species have sharp-angled triangular stems, and keeled leaves which clasp the stem at their base, and are sometimes cleft along the keel.
The syncladeous Sphagnei are aquatic bog mosses of a pale yellowish green colour. They form but one genus, Sphagnum, which consists of some eight or ten species and several varieties. The species of Sphagnum, or common bog moss, hold an important place in the economy of nature. They are floating mosses, entirely destitute of roots. The stalk of the full grown plant, like that of land mosses, is constructed of three kinds of cells; one forms the exterior or cortical layer, another forms the central pith or axial system, while the third, which is coloured and somewhat ligneous, comes between the other two. The leaves, which have their origin in the cortical layer while it is yet soft, consist of two kinds of cells, one kind being large, elongated, and colourless, and containing spiral fibres loosely coiled in their interior. The membranous walls of these cells have large round apertures by which their cavities have free communication; for certain animalcules, which sometimes live in the cells, have been seen to pass from one to the other. Between these colourless cells are some thick-walled, narrow, elongated green cells, which give the leaf firmness and colour. According to Mr. Wilson, the fascicles, or bundles of branches, are disposed round the stem in imbricated spirals, so that, for every complete spiral formed by five of these fascicles, there are eight spirals formed of twenty leaves, four leaves being inserted between each pair of fascicles. The fructification in all these floating mosses is immersed in the leaves of the stem, the antheridia being globose, and the spermatozoids having spiral motions, both within the cells of the antheridia and when they come out. The urns, which are the product of fructification, and are borne at the top of what appears to be a long footstalk, but is in reality a pedunculate vaginula, are globular, and their lids have been observed to be driven off when the spores are ripe, with such force as to give a distinctly audible report.
The common bog moss grows so rapidly that, rootless as it is, it soon covers a pool with its matted bundles of branches, and as in a few years it has no room to spread, the lower stems and branches decay, sink to the bottom, and begin to form a peat moss, while the upper parts grow on, so that new stems and branches are perpetually produced. Multitudes of spores no doubt germinate, and, in this way, the pool is filled up, and a peat moss is at length formed.
The Sphagnum moss has such a power of absorbing moisture from the atmosphere, that it forms and maintains the peat mosses and quagmires in the mountains which feed the streams at their feet. Mosses in general are almost as much indebted for moisture to the absorbing nature of their leaves as to their roots; but the loose, large celled, and perforated leaves of the Sphagnum suck up water like a sponge; even during the heat of summer, a quantity of water may be squeezed out of a handful of them. In fact the plant is a perfect hydraulic machine, for a small stem of it put into a glass of water with its drooping terminal branch hanging over the edge, acts like a syphon, and soon empties the glass, pouring the water out through its bending top. Though the peat from Sphagnum is often too spongy for fuel at present, yet that little moss now growing on our mountains will yield aniline, magenta, paraffin, and other illuminating gases to remote generations, although not in such quantities as the richer vegetation of the coal measures, the products of a warmer period.
Like all cryptogams the mosses are exceedingly variable and difficult to distinguish. Not only does the same species show great differences in size, but even in other respects the characters vary on account of climate, soil, and exposure.
Beyond that of becoming converted into peat, the uses of the moss family are not of any great importance. Brooms, mats, and other domestic articles are sometimes formed from Polytrichum, and in Lapland Sphagnum not only sometimes enters into the composition of bread, but is used in place of clothing for new-born babes.
SECTION VIII.
FILICES, OR FERNS.
Of all the spore-bearing families, the Ferns are the most universally known. They may easily be recognized by the coiling inwards of their young leaves in spring previous to expansion, and by the arrangement of the fruit on their undersides when expanded. The Ferns are exceedingly numerous both in genera and species, and vary from low herbaceous plants of an inch high, to trees with upright trunks forty or fifty feet or more in height, bearing a graceful coronet of leaves at their extremity. The tree ferns come to the utmost perfection in the warm, moist islands of the tropical oceans. Their boreal limit is about the thirty-seventh parallel of north latitude, but, on account of the vast extent of ocean in the southern hemisphere, they reach the fortieth or fiftieth parallel of south latitude, the more copious evaporation, and the consequently moister air and soil, being specially congenial to the fern tribe. For that reason a most luxuriant fern vegetation prevails in Juan Fernandez, Western Chili, and New Zealand. In the latter there are one hundred and twenty species, some of which are subarborescent, while others form tree ferns of considerable altitude. Shade is not absolutely requisite to ferns, for many of them grow luxuriantly when exposed to the sun, provided the soil be damp.
The range of the non-arborescent ferns is very extensive. According to Dr. J. D. Hooker, twenty-one species have been found in Fuegia and the Falkland Islands, and one grows in matted tufts in Kerguelen’s Land. In the north the Cytopteris fragilis has been found in the seventieth parallel of latitude at Minto Inlet, and both it and Polystichum Lonchitis have been gathered at Disco, on the west side of Greenland, and Aspidium fragrans on the eastern side.