. Elements of biology; a practical text-book correlating botany, zoology, and human physiology. Biology. 156 BOTANY others the veins bear the spore cases, while in some ferns the entire leaf is modified into a spore-bearing organ. The Horsetails.—This comprises a small group of plants, recognized by their erect habit of growth, the leaves coming out in whorls on the stem. In most forms the stem contains considerable silica. This gave to the plant its former use- ful place in the household and its name of the scouring rush. If you burn one of these plants very carefully on a tin plate over a ve
. Elements of biology; a practical text-book correlating botany, zoology, and human physiology. Biology. 156 BOTANY others the veins bear the spore cases, while in some ferns the entire leaf is modified into a spore-bearing organ. The Horsetails.—This comprises a small group of plants, recognized by their erect habit of growth, the leaves coming out in whorls on the stem. In most forms the stem contains considerable silica. This gave to the plant its former use- ful place in the household and its name of the scouring rush. If you burn one of these plants very carefully on a tin plate over a very hot fire, the delicate skeleton of silica may be seen. The horsetails, or Equisetums, were once a very important part of the earth's vegetation. Before the coal fields were formed the ancestors of these plants flourished as trees. A large amount of the coal of this country is undoubtedly formed from the trunks of the Equisetums of the Carboniferous age. At present they are represented by a very few species, none of which are over four or five feet in height. Club Mosses.—Another relative of the fern is the club moss {Lyco'podium). It is familiar to us as a Christmas decoration under the name of ground pine. It is chiefly of interest now as the representative of another group of plants that flourished during the Carboniferous age. Economic Value of Ferns. — It maybe said that the ferns as a group have formed a large part of the enormous deposits of almost pure carbon that we call coal, from which we now derive the energy to run our many en- gines. Bryophytes. An eqmsetum, about one half natural size. Mosses, like ferns, are shade-loving and moisture-loving plants. They form velvety carpets in many of our forests, but they often show their preference for moist localities by cover- ing the wooded shores of lakes and swamps. Pigeon-wheat Moss. — One of the mosses frequently seen and easily recognized is the so-called pigeon-wheat moss {Polytrichum. Please note that these
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