Mosses and Lichens
No frequenter of the woods can be unfamiliar with the more conspicuous lichens and mosses. It is with them that nature adorns her bare unsightly children. She drapes the timeworn evergreens with gray fringes and decks the old tree-stumps with red or yellow corals. Soft lichens spread over the ground in the deep shade of the pine trees, while pale green or yellow rosettes creep over the fence-rails and the big rocks in the pasture lot.
Lichens and mosses are met with all over the world, in the cold North and in the sunny South, in the East and in the West, by the seashore and on the highest mountain peaks. They are the first growths to appear on the rocks and in the places which give no foothold to other plants. When the side of a mountain is torn away by frosts and floods, and the bared rocks, shorn of their forest trees and shrubs, are left unsightly with nothing to tempt other plants to make a home on their ledges, then the lichens come and cover the bared cliffs with delicate traceries and mantles of exquisite grays and greens. They need no soil, a polished rock will meet their need.
Who has not loved the mossy banks and the little velvet cushions which cling to the plaster of the old wall or spring up in the crevices of the pavement, giving restful spots of green to the dreary monotony of brick and stone? Children play with mosses and lichens. Poets sing their charms. Artists endeavor to reproduce their wonderful colors traced on bark and rock.
Aside from their artistic charm, mosses and lichens have other charms for all who will pause awhile to study their habits, and for all who will linger long enough to make out what the plants are doing in their humble way. They have wonderful mechanical contrivances for the physicist, curious processes of interest to the chemist, and many suggestions for the philosopher.
If plants are small and green, with leafy stems, and have the habit of living in such close proximity as to form velvety cushions, (Ceratodon purpureum) one may suspect them of being mosses, but if they have this habit of growth, or grow in clusters resembling tiny ferns or miniature trees and bear their spores in little cases opening by lids, one may feel confident that they are the true mosses as distinguished from hepatics.
All true mosses produce their spores in a spore-case of one shape or another which opens, with few exceptions, by a lid. The spore-case may be situated at the summit of the stem of the moss-plant or on one side of the stem. It may or may not be supported upon a pedicel (seta).
Many species of moss have two rows of teeth about the rim of the spore-case, while some have one row and some have none. The teeth may vary greatly in shape and number; as a rule, there are four, sixteen, thirty-two or sixty-four.
The foothold of the lichens is often so insecure that one must exclaim as he sees them, “How do you grow in such unfavorable places? On what do you subsist? No soil! No water! Dry as tinder! Crumbling at any rude touch! “If the plant could answer, no doubt it would say, “There must be pioneers to open up new territory for higher plants, so from the earliest times nature has employed us to do this work. We travel swiftly as the wind for we travel with the wind. We are fed by the rains and the dews, the hard rocks soften at our touch and give us food.”
It is true that these little plants as they lie upon the rocks, secrete an acid which dissolves the hard minerals. It is true that they have the power to condense moisture from the air, however little it may be, for they must have water as an item of food and as a medium by which mineral salts dissolved from the rocks may enter the interior of the plant and may pass from cell to cell to those parts where they are to be worked up into plant food.
The lichens are often the forerunners of rock-loving mosses as without the scanty soil prepared by their chemical action and, without the slight foothold which their debris afford, many mosses would be unable to get a start upon the forbidding rock.
Liverworts or Hepatics
If the plants are green, growing flat and ribbon-like or as prostate stems with paired, veinless leaves and with fruits umbrella-like or cups which do not open by lids but split irregularly into symmetrical valves in order to permit their spores to escape, one may know them to be hepatics.
The beauty which mosses lend to the surfaces upon which they live is pretty generally conceded. One has but to recall the frequent reference which our poets make to them to feel that they have always appealed to the poetic eye.
Liverworts are as a rule found only in damp shady places, and it is not their habit to occupy very large areas of ground. With but few exceptions the plant lies close to the object upon which it grows holding to it by short hair-like cells (rhizoids).
Excepting the fruiting portion, the liverwort plant (the vegetative body) is either ribbon-like (thalloid), or a stem with scalelike leaves ( foliose); the greater number of liverworts are therefore distinguished as thalloid and foliose.