strand of tissue, the columella, which expands at the mouth into a thin, membranous disk, closing the entire mouth of the capsule except the narrow annular chink guarded by the teeth. In this moss the points of the teeth are attached to the margin of the membrane, allowing the spores to sift out through the spaces between them.
When the spores germinate they form a green, branched thread, the protonema. This gives rise directly to moss plants, which appear as little buds on the thread. When the moss plants have sent their little rhizoids into the earth, the protonema dies, for it is no longer necessary for the support of the little plants, and the moss plants grow independently.
Funaria is a moss very common on damp, open soil. It forms green patches of small fine leaves from which arise long brown stalks terminated by curved capsules (Fig. 298). The structure is similar to that of polytrichum, except the absence of plates on the under side of the leaves, the continuous growth of the stem, the curved capsule, double peristome, monœcious rather than diœcious receptacles, and nearly glabrous unsymmetrical calyptra.
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Fig. 298.—Funaria hygroscopica.
Equisetums, or Horsetails (Pteridophyta)
There are about twenty-five species of equisetum, constituting
the only genus of the unique family Equisetaceæ. Among these
E. arvense (Fig. 299) is common on clayey and sandy soils.
In this species the work of nutrition and that of spore production are performed by separate shoots from an underground rhizome. The fertile branches appear early in spring. The stem, which is 3 to 6 inches high, consists of a number of cylindrical, furrowed internodes, each sheathed at the base by a circle of scale leaves. The shoots are of a pale yellow color. They contain no chlorophyll, and are nourished by the food stored in the rhizome (Fig. 299).
The spores are formed on specially developed fertile leaves or sporophylls which are collected into a spike or cone at the end of the stalk (a, Fig. 299). A single sporophyll is shown at b. It consists of a short stalk expanded into a broad, mushroom-like head. Several large sporangia are borne on its under side. The spores formed in the sporangia are very interesting and beautiful
