General structure of bryophytes: They show alternation of generation. Gametophyte: The dominant generation in bryophyte is gametophyte. It is vegetative plant body. It has smaller size. The plants are multicellular and have simple thallus. Some may be differentiated into simple leaves and stem. Vascular tissues (xylem and phloem) are absent in them. Roots are absent and rhizoid performs the function of water absorption. Rhizoid fixing the plant to soil. Rhizoid may be unicellular or multicellular and have thread like structure. Leaves usually single layered and attached to stem. Stem is short, unbranched and lacking vascular tissues. Male reproductive organs are antheridia and female reproductive organs are archegonia. The gametophytic plants are independent and have chloroplast for photosynthesis. The cells of gametophyte are haploid. Sporophyte is totally or partially dependent on gametophyte for its nourishment. It has simple structure and differentiated into foot, seta and capsule. Capsule contains spores. The cells of sporophyte are diploid. Sporophyte is spores producing structure. Reproduction: Vegetative reproduction: Vegetative reproduction is common in bryophytes and occurs during favourable growing season. It occurs only in the gametophytic stage and takes place by parts of vegetative plant or by the production of special vegetative propagules. Sexual reproduction: Sexual reproduction is oogamous and sex organs are always produced on gametophyte. Male reproductive organs are antheridia and female reproductive organs are archegonia. Male gamete is antherozoid and it is motile. Female gamete is nonmotile oosphere. Oosphere is not free from female gametangia. Both sex organs are multicellular structures. They are borne on short multicellular stalks and develop a jacket of sterile cells. Antherozoids or spermatozoids are biflagellate structure with a long coiled body. The antheridium has androgonial cells. These cells give rise to androcytes or antherozoid mother cells. Androcytes give rise to antherozoids. Archegonia are flask shaped structures. The basal swollen portion of the archegonium is called venter and the upper elongated part is the neck. The venter contains female gamete or oosphere or egg and oosphere is not released from archegonium. A small cell is present upper to the oosphere in venter called venter canal cell. The neck of archegonium contains row of cells called the neck canal cells. When the archegonia are mature the venter canal cells and neck canal cells disintegrate. It makes the passage for the entry of antherozoids. Fertilization: The antherozoid fuse with oosphere during fertilization and forms diploid oospore. Oospore is develop into the sporophyte. Classification: Bryophytes are divided into three division. Hepaticopsida (Liverworts): Liverworts are the simplest bryophytes and they grow on moist rocks and wet soil. Their plant body is gametophyte and there are two forms of gametophyte. Some have thallus body. Thallus is flat or ribbon like structure and it is attached to soil by rhizoids for example; Marchantia. Some have plant like body. In this case plant body grows upright and it has false leaves. Its stem is differentiated into false stem and leaves for example; Porella. The sex organs develop near the tips of branches on the upper surface of thallus. Sometimes, sex organs are developed on special branches of gametophyte called antheridiophore and archegoniophore as in Marchantia. The sporophyte is dependent on gametophyte. Bryopsida (Mosses): Mosses live in damp places. The adult plant body of moss is gametophyte and gametophyte has stem and leaves like structures. Their reproductive organs develop on tips of different branches. The archegonium and antheridium form clusters. They are mixed with hairs called paraphyses. They show alternation of generation. The spore of mosses produces algae like structure called protonema. Examples of mosses are Funaria and Polytrichum. Anthoceropsida: They are slightly advanced than liverworts and mosses. Their gametophyte is highly lobed and it has irregular outline. Antheridia and archegonia are partially sunken in gametophyte tissues. Sporophyte does not depend on gametophyte for nourishment and protection, except in the early stage of development. Sporophyte shows many advance character, so it can easily grow on land as compared to other bryophyte groups. Sporophyte has stomata and chloroplast in epidermis, so it can prepare its own food by photosynthesis. It does not obtain food from gametophyte. It also has a band of meristematic tissues at the junction of foot and spore producing region and there is fast growth of these meristematic tissues. So length of sporophyte continues to increase for an indefinite period of time. In this way, sporophyte survives even after death and decay of the gametophyte. Examples of anthoceropsida are Anthoceros and Megaceros.
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