Moss

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Moss is a common name for members of a division of plants (see Bryophytes). Mosses grow on soil, rocks, and the bark of trees, and in bogs and shallow streams. Moss plants consist of small, slender stalks and leaves; vascular tissue is not present. They lack true roots, the functions of underground support and conduction being carried on by filamentous structures called rhizoids. The organs of sexual reproduction, called antheridia and archegonia, contain sperms and egg, respectively, and are borne on the gametophyte, which is an independent leafy plant. Fertilization can take place only when the plants are wet; after fertilization, the egg grows into a sporophyte. The sporophyte consists of a base, or foot, embedded in gametophyte tissue; a stalk that is usually long and hairlike; and a terminal capsule. The capsule, which in most species is covered by a small-toothed lid, contains numerous spores. The spores are either released explosively or by special peristome teeth. Under suitable conditions they germinate by forming slender underground filaments called protonemata. Small buds produced by protonemata give rise to gametophyte plants. Mosses also produce gametophytes from such specialized vegetative organs as bulbils, produced by rhizoids; gemmae, produced on leaves or stems; and secondary protonemata, produced by rhizoids or wounded portions of the leafy shoot (see Alternation of Generations). The division is commonly divided into three classes: the liverworts, the hornworts, and the mosses.

Scientific classification: Mosses make up the division Bryophyta. The liverworts make up the class Hepaticae, the hornworts the class Anthocerotae, and the mosses the class Musci.

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