The moss plant is the first plants to colonise land, and have probably evolved from the green algae as per classification they are called bryophytes. Although bryophytes have developed some protective structures, they are not eminently suited to a terrestrial existence. They require moist atmosphere, particularly for their reproductive cycles. In general, moss plant are confined to damp, shady places.
The life-cycle of moss plant is characterized by regular alternation of two morphologically distinct phases—a gametophytic phase and a sporophytic phase. The gametophytic plant body, which forms the leading phase in the life-cycle, is generally small, attaining a length of a few centimeters, but some kind reach up to 70 cm in length. The sporophytic phase is, however, short-lived and completely dependent upon the gametophyte. True roots are not present in moss plant and the function of waterfront and absorption is performed by filamentous structures known as rhizoids. The moss plant body is composed of parenchymatous cells only and lacks fully differentiated xylem and phloem, which is characteristic of vascular plants.
Reproduction of Moss Plant
The moss plant reproduces by vegetative and sexual methods. Vegetative multiplication takes place by death and decomposes of old parts of the thallus, by adventitious branches or by special structures like tubers, gemmae, etc. Sexual reproduction is of oogamous type and sex organs are multicellular structures. The male sex organs, known as antheridia, are stalked, globose or somewhat elliptic structures. They have an outer barren one cell thick jacket which surrounds a solid mass of fertile cells, the androcytes. Each androcyte finally metamorphoses into a motile biflagellate antherozoid. The female sex organ, known as archegonium, is a flask shaped structure, with a basal swollen Venter and upper slender neck.
Water is essential for fertilization. By the fusion of antherozoid and egg, a diploid zygote is formed. The zygote does not have any inactive period and it develops into a sporophyte. The sporophyte is completely dependent upon the gametophyte. It is a foretelling structure, differentiated into foot, seta and capsule. But sometimes the sporophyte is represented either only by capsule such as, Riccia or by foot and capsule such as, Corsinia. The sporogenous cells present in the capsule form many haploid spores after reduction division. All spores are similar in shape and size. They are non-motile and distribute exclusively by wind. Under favorable conditions, the spore either forms a filamentous germ tube which divides to form a young gametophyte such as, Riccia or give rise to a protonema as in mosses. The protonema bears many buds which develop into erect gametophores. Thus, in moss plant, a haploid gametophytic generation and a diploid sporophytic generation alternate in the life cycle.
Economic Importance of Moss Plant
Moss plant along with lichens is the pioneer in establishing vegetation at such places where it is almost impossible for other plants to grow. They prevent soil erosion by holding the soil by their extensive carpets. The moss Sphagnum that generally occurs in bogs, can absorb large amounts of water. It is thus used by gardeners to keep cut plant parts moist during transportation and proliferation. Peat from peat mosses (Sphagnum) is the source of coal and used as fuel. Sphagnonal, an antibiotic from peat moss is effective against Gram positive and Gram negative bacteria. Thus the moss plant has so many economical significances for mankind.