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.