Life Cycle of Bryophyte

Bryophytes are a group of land inhabiting plants which are simple and primitive in nature. They are generally restricted to moist and shady places such as in bogs, on damp rocks and trees, by the side of pools and streams, and in deep humid wood. Although, the members of bryophytes have adapted to land conditions, they still require external water supply for completing their life cycle. Hence, they are also called 'amphibious plants.' In the life cycle of a Bryophyte, there is a definite alternation of a gametophytic and a sporophytic generation.

Protonema

• The life of a bryophyte begins from a spore which germinates and produces a protonema. Protonema is either filamentous or thalloid. It looks like a slim green felt. Apical cells undergo differentiation and produce the foliose shoots at different places of the Protonema. This is a transitory stage in the life cycle of a bryophyte because protonema soon develops into the gametophore.

Gametophore

• An apical cell produces stems or branches which lead to the development of sex organs of the bryophyte. The stems produce leaves and branches spirally arranged. The leaves are simple, unlobed and attached directly by the base, not having an intervening stalk. Other outgrowths to the stem include auxiliary hairs, multi-cellular rhizoids, paraphyllia, and many other asexual propagules.

Gametangia

• The female organs are termed as archegonia and surrounded by a series of modified leaves celled 'perichaetum' (plural, perichaeta). The archegonia has a sterile jacket and usually differentiated into bulbs celled 'venter'. The male organs are termed as antheridia and are also protected by a group of modified leaves similar to the archegonia.

Seta

• The sporophyte body is comprised of a long stalk, known as 'seta', a haustorial foot, and a capsule protected by a cap called apical sporangium. The foot is engrafted within the top of a stem or branch. The seta is either short or elongated containing an internal conducive system that links between the foot and the apical sporangium at both sides.

Sporangium

• A single, multi-cellular sporangium or capsule develops at some distance from an undifferentiated sporophyte. The sporangium opens up by longitudinal splits of apical pores. The outer layer contains stomata, particularly in the neck, and the underlying exothecium layer is made up of parenchymatose cells.

Peristome

• At the final stage of life cycle of bryophyte, the apex of the capsule dislodges after metamorphosis and forms a structure, known as peristome. There are two basic types of peristomes that are seen in bryophyte: nematodontous and arthrodontous.