So far, then, we now understand the growth of the mossy-leaf stems, but this is only half the life of the plant. After the moss has gone on through the damp winter spreading and growing, there appear in the spring or summer tiny moss flowers at the tip of some of the stems. These flowers (a, p, Fig. 34) are formed merely of a few green leaves shorter and stouter than the rest, enclosing some oval sacs surrounded by jointed hairs or filaments (see A and P, Fig. 35). These sacs are of two different kinds, one set being short and stout os, the others having long necks like bottles bs. Sometimes these two kinds of sac are in one flower, but more often they are in separate flowers, as in the hair-moss, Polytrichum commune (a and p, Fig. 34). Now when the flowers are ripe the short sacs in the flower A open and fling out myriads of cells zc, and these cells burst, and forth come tiny wriggling bodies z, called by botanists antherozoids, one out of each cell. These find their way along the damp moss to the flower P, and entering the neck of one of the bottle-shaped sacs bs, find out each another cell or ovule inside. The two cells together then form a plant-egg, which answers to the germ in the seeds of higher plants.
Now let us be sure we understand where we are in the life of the plant. We have had its green-growing time, its flowering, and the formation of what we may roughly call its seed, which last in ordinary higher plants would fall down and grow into a new green plant. But with the moss there is more to come. The egg does not shake out of the bottle-necked sac, but begins to grow inside it, sending down a little tube into the moss stem, and using it as other plants use the ground to grow in.
As soon as it is rooted it begins to form a delicate stem, and as this grows it pushes up the sac bs, stretching the neck tighter and tighter till at last it tears away below, and the sac is carried up and hangs like an extinguisher or cap (c Figs. 34, 35) over the top of the stem. Meanwhile, under this cap the top of the stalk swells into a knob which, by degrees, becomes a lovely little covered urn u, something like a poppy head, which has within it a number of spores. The growth of this tiny urn-plant often occupies several months, for you must remember that it is not merely a fruit, though it is often called so, but a real plant, taking in food through its tubes below and working for its living.
When it is finished it is a most lovely little object (us, Fig. 34), the fine hairlike stalk being covered with a green, yellow, or brilliant red fool's cap on the top, yet the whole in most mosses is not bigger than an ordinary pin. You may easily see them in the spring or summer, or even sometimes in the winter. I have only been able to bring you one very little one to-day, the Funaria hygrometrica, which fruits early in the year. This moss has only a short cap, but in many mosses they are very conspicuous. I have often pulled them off as you would pull a cap from a boy's head. In nature they fall off after a time, leaving the urn, which, though so small, is a most complicated structure. First it has an outer skin, with holes or mouths in it which open and close to let moisture in and out. Then come two layers of cells, then an open space full of air, in which are the green chlorophyll grains which are working up food for the tiny plant as the moisture comes in to them. Lastly, within this again is a mass of tissue, round which grow the spores which are soon to be sown, and which in Polytrichum commune are protected by a lid. Even after the extinguisher and the lid have both fallen off, the spores cannot fall out, for a thick row of teeth (t, Fig. 35) is closed over them like the tentacles of an anemone. So long as the air is damp these teeth remain closed; it is only in fine dry weather that they open and the spores are scattered on the ground. Funaria hygrometrica has no lid under its cap, and after the cap falls the spores are only protected by the teeth.
When the spores are gone, the life of the tiny urn-plant is over. It shrivels and dies, leaving ten, fifteen, or even more spores, which, after lying for some time on the ground, sprout and grow into a fresh mass of soft threads.
So now we have completed the life-history of the moss and come back to the point at which we started. I am afraid it has been rather a difficult history to follow step by step, and yet it is perfectly clear when once we master the succession of growths. Starting from a spore, the thread-mass or protonema gives rise to the moss-stems forming the dense green carpet, then the green flowers on some of the leaf-stems give rise to a plant-egg, which roots itself in the stem, and grows into a perfect plant without leaves, bearing merely the urn in which fresh spores are formed, and so the round goes on from year to year.
There are a great number of different varieties of moss, and they differ in the shape and arrangement of their stems and leaves, and very much in the formation of their urns, yet this sketch will enable you to study them with understanding, and when you find in the wood the nodding caps of the fruiting plants, some red, some green, some yellow, and some a brilliant orange, you will feel that they are acquaintances, and by the help of the microscope may soon become friends.
Fig. 36.
Sphagnum moss from a Devonshire bog. (From life.)