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Ferns. A natural order of cryptogamous or flowerless plants, forming the highest group of the acrogens or summit growers. They are leafy plants, the leaves, or more properly fronds, arising from a rhizome or root stock, or from a hollow arborescent trunk; they are circinate in vernation, a term descriptive of the manner in which the fronds are rolled up before they are developed in spring, having then the appearance of a bishop's crosier. Ferns have a wide geographical range, but are most abundant in humid, temperate, and tropical regions. In the tropical forests the tree ferns rival the palms, rising sometimes to a height of thirty-five to forty-five feet. Ferns are very abundant as fossil plants. The earliest known forms occur in Devonian rocks. Various systems of classification for ferns have been proposed. At present the order is usually divided into six or eight families distinguished by differences in the position and structure of the sporangium. The generic characters are founded on the position and direction of the sori and on the venation. The largcst division is that of the Polypodiacece, to which belong most of the herbaceous ferns of the temperate regions. A few of the ferns are used medicinally, mostly as demulcents and astringents.

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