Page:The American Cyclopædia (1879) Volume VII.djvu/158

 150 FERNS recognizing as many as eight, founded upon the structure, manner of attachment, and mode of opening of the sporangia. By far the largest of these suborders is the polypodiacece, or true ferns, which includes the great majority of those with which we are familiar in the wild Rock Fern (Polypodium vulgare). state or in cultivation. In ferns of this sub- order the structure of the. sporangium is curious. A little bundle of cellular pores on a stem of the same cell formation is clasped around by a ring of thick and elastic segments, each resembling a U with the rounded part in- ward and the sides united. While the sporan- gium is alive and full of sap the arms of the (J Hart's Tongue (Scolopendrium officinarum). remain almost parallel; but as the ring dries the arms shrink together, and the capsule is ruptured, often with force enough to throw the minute spores to some distance. The position of the sporangia on the frond is an import- ant generic distinction. In the common rock fern (polypodium) they are round, cinnamon- colored dots in rows each side of the midrib ; hart's tongue (scolopendrium) they form in numerous obliquely transverse lines ; in maiden- hair (adiantum) a bit of the edge of the frond folds over the capsules ; in the brake (pteris) Maiden-hair (Adiantum pedatum). the whole edge is folded over; and in the asplenium and many other ferns the sporangia are in oblong masses pinnately arranged each side of the midrib of the smaller divisions of the frond. In hymenopliyllum, of a different suborder, the capsules are contained in a calyx- like urn springing from the terminal veins. In the ophioglossacece, which include our com- Common Brake (Pteris aquilina). mon adder's tongue and moon wort, the spo- rangia are entirely without the elastic ring, and open by a transverse slit into two valves. The spores are very minute and of various shapes, and form the brown (rarely green) dust which falls when a ripe frond is shaken. The mode