Among them one of the most interesting is the sphagnum or bog-moss (Fig. 36), which spreads its thick carpet over all the bogs in the woods. You cannot miss its little orange-coloured spore-cases if you look closely, for they contrast strongly with its pale green leaves, out of which they stand on very short stalks. I wish we could examine it, for it differs much from other mosses, both in leaves and fruit, but it would take us too long. At least, however, you must put one of its lovely transparent leaves under the microscope, that you may see the large air-cells which lie between the growing cells, and admire the lovely glistening bands which run across and across their covering membrane, for the sphagnum leaf is so extremely beautiful that you will never forget it when once seen. It is through these large cells in the edge of the stem and leaf that the water rises up from the swamp, so that the whole moss is like a wet sponge.
And now, before we part, we had better sum up the history of lichens and mosses. With the lichens we have seen that the secret of success seems to be mutual help. The green cells provide the food, the fungus cells form a surface over which the green cells can spread to find sunlight and moisture, and protection from extremes of heat or cold. With the mosses the secret lies in their standing on the borderland between two classes of plant life. On the one hand, they are still tender-celled plants, each cell being able to live its own life and make its own food; on the other hand, they have risen into shapely plants with the beginnings of feeble roots, and having stems along which their leaves are arranged so that they are spread to the light and air. Both lichens and mosses keep one great advantage common to all tender-celled plants; they can be dried up so that you would think them dead, and yet, because they can work all over their surface whenever heat and moisture reach them, each cell drinks in food again and the plant revives. So when a scorching sun, or a dry season, or a biting frost kills other plants, the mosses and lichens bide their time till moisture comes again.
In our own country they grow almost everywhere—on walls, on broken ground, on sand-heaps, on roofs and walls, on trees living and dead, and over all pastures which are allowed to grow poor and worn out. They grow, too, in all damp, marshy spots; especially the bog-mosses forming the peat-bogs which cover a large part of Ireland and many regions in Scotland; and these same bog-mosses occur in America, New Zealand, and Australia.
In the tropics mosses are less abundant, probably because other plants flourish so luxuriantly; but in Arctic Siberia and Arctic America both lichens and mosses live on the vast Tundras. There, during the three short months of summer, when the surface of the ground is soft, the lichens spread far and wide where all else is lifeless, while in moister parts the Polytrichums or hair-mosses cover the ground, and in swampy regions stunted Sphagnums form peat-bogs only a few inches in depth over the frozen soil beneath. If, then, the lichens and mosses can flourish even in such dreary latitudes as these, we can understand how they defy even our coldest winters, appearing fresh and green when the snow melts away from over them, and leave their cells bathed in water, so that these lowly plants clothe the wood with their beauty when otherwise all would be bare and lifeless.
[1] Confervæ.
[2] Oscillariæ.
[3] Protococcus.
[4] Palmella cruenta.
[5] Protococcus nivalis.
[6] Nostoc.