FERNS and The ferns are representatives of an extensive branch of the plant world technically known as pterido phytes, standing between the mosses and hepatics (bryophytes) on the one hand and the cycads and conifers (gymnosperms) on the other, at the head of the now obsolete subdivision of plants known as cryptogams. They resemble the former groups so closely in their method of sexual reproduction and in showing alternating phases of growth that both mosses and ferns are often united under a single primary division of plants as archegoniates, so called from -the common possession of a structure described be low as the archegone. The ferns differ from the mosses in their highly developed vascular or woody system seen in the fibrous strands of the leaf-stalks and the veins of the leaves, and so are still sometimes called vascular crypto gams. Besides the ferns, popularly so known, there are various groups of plants. closely allied to ferns which with them make up the branch pteridophytes. Among these fern-allies are the running-pine or ground-pine, familiar in its use for Christmas decoration, the selaginellas fre quent in cultivation, the field horsetail and the scouring-rush. These will be treated in their proper sequence below.
The mature fern-plant, which may stand as a representative pteridophyte, consists of a woody axis bearing scattered or clustered leaves ac cording as this axis is a creeping structure or an upright trunk. In our northern species this axis is either below the surface of the ground or just at the surface, but in some of the spe cies of tropical regions it often forms a trunk from 1 foot to 50 feet in height, or even more, bearing its leaves at the summit and forming a treefern.
On the under surface of certain leaves of ordinary ferns little clusters of stalked bodies (sporangia) appear, which are variously ar ranged in different species, in rounded or linear masses (sori) or in a few species are scattered over the surface of the leaf. These structures consist of a membraneous wall enclosing minute bodies — the fern-spores. These are the re productive bodies of the fern asexually pro duced by repeated division of the interior por tion of the young sporangium, and are often popularly known as *fern-seeds? This is a misnomer, for they rather find their homology with the pollen-grains and young embryosacs of the higher plants. In the sporangia of some
ferns a series of peculiar cells serves the pur pose of rupturing the sporangium wall, and by an elastic movement scatters the spores at some distance from the plant producing them. Either at once or after a period of rest the fern-spore sprouts and produces a green hepa tic-like structure known as a prothallus. This is a flat expense of soft green tissue, usually more or less heart-shaped, and ranging up to a half inch or more in diameter. It forms root-hairs beneath, and grows exactly like an ordinary new plant. On its under surface among the root-hairs two sorts of structures are produced: (1) A series of rounded bodies known as antherids, in which minute motile cells are formed known as antherozoids, these being the male or sperm cells connected with the sexual reproduction of the fern; (2) a series of flask-shaped bodies (archegones) more deeply imbedded in the tissues of the pro thallus, which contain a single specialized cell at the bottom of the flask, known as the egg, this being the female reproductive cell. The sperm-cells escaping from the antherid swim in the delicate film of moisture which may bathe the surface of the prothallus, swarm about the mouth of the archegone, and one of them enters the neck of the flask-like structure, penetrating the mucilaginous contents of its tube, and fuses with the egg, thus effecting a true sexual reproduction. The fertilized soon commences division, increases in size all develops a primary root and leaf, ultimately growing into a new fern-plant. The two alter nating phases of growth in the life period of the fern are thus strongly marked; the sexual phase (prothallus) is often known as the irk metophyte, and the asexual phase (the fern plant) which follows is known as the sporo phyte or spore-producing phase.