Page:Popular Science Monthly Volume 25.djvu/172

152 Fig. 6 is seen a vertical section of one fully grown, showing the various parts of theca, calyptera, operculum, etc. In this complicated sporangium, small spores in great numbers are produced, and with their perfection ends the last chapter in the life-history of the moss.



The spore produces a fine filamentous growth, from which the true moss-plant develops. This is the sexual generation, and from fertilized germ-cells, which it bears, the asexual generation is produced, consisting of the spore-case, its stalk, and, most important of all, the many spores.

We now come to a more exalted group of plants, and the first of the cryptogams with spiral vessels and other ducts in the wood. The ferns are so familiar to all that any description of their general appearance is unnecessary. The first generation proceeds directly from the spore, and consists of a simple green expansion which is short-lived and very small, not usually exceeding half the size of a small finger-nail. This prothallus, as it is termed, has small, root-like hairs which fix it to the earth or elsewhere. The prothallia are to be seen in large numbers on the sides of flower-pots in neglected greenhouses. Each little green scale is a young fern-plant during its sexual generation. The male and female organs are much the same shape as those of mosses.