In no tribe of plants is there so great a similarity between the different species as in the mosses. This remarkable similarity, concealing a no less remarkable diversity, has led to the popular belief that there is only one kind of moss. Closely examined, however, by an educated eye, their exceeding variableness of form will at once become evident, some being slender, hair-like plants; some resembling miniature fir-trees, others cedars, and others crested feathers and ostrich-plumes. In size they vary from a minute film of green scarcely visible to the naked eye to wreaths and clusters several feet in length. Nor are their colors less variable, ranging from white through every shade of yellow, red, green, and brown, to the deepest and most sombre black. The leaves of mosses are their most prominent parts. To the careless and superficial eye, accustomed to look at a tuft of moss as merely a patch of velvety greenness, creeping over an old tree or dike, the leaves of all mosses may appear precisely similar; but the attentive observer who examines them under a microscope will find that the leaves of different kinds of trees are not more distinct from each other than are those of the mosses. The organs of fructification, however, with which mosses are furnished, are, perhaps, the most wonderful parts of their economy. When the requisite conditions are present, these are generally developed during the winter and spring months, and may be easily recognized by their peculiar appearance. At first a forest of hair-like stalks, of a pale pink color, rises above the general level of the tuft of moss to the height of between one and three inches, giving to the moss the appearance of a pincushion well provided with pins. These stalks, through course of time, are crowned with little wen-like vessels called capsules, which are covered at an early stage with little caps, like those of the Normandy peasants, with high peaks and long lappets--in one species bearing a remarkable resemblance to the extinguisher of a candle--a curious provision for protecting them alike from the sunshine and the rain, until the delicate structures underneath are matured. When the fruit-stalk lengthens and the capsules swell, this hood or cap is torn from its support and carried up on the top of the seed-vessel, much in the same way as the common garden annual, the Eschscholtzia or Californian poppy is borne up on the summit of the cone-like petals before they expand. When the seed-vessel is riper it falls off altogether, and discloses a little lid covering the mouth of the capsule, which is also removed at a more advanced stage of growth. The mouth of the seed-vessel is then seen to be fringed all round with a single or double row of teeth, which closely fit into each other, and completely close up the aperture.