General characters of bryophytes

General characters of bryophytes

1. General characters of Bryophytes Dr. Dhole Nagesh Arjunrao Department of Botany, Digambarrao Bindu ACS College, Bhokar

2. Habit: The bryophytes are very small, green leafy or thalloid plant body. Habitat: Bryophytes are mostly primitive amphibian thallophytes . They generally grow on damp, shaded, humid localities. Vegetative structure completely adapted to the land but during sexual reproduction water is essential for sperms to swim towards the female gamete for fertilization and their development processes . Plant body: The plant body is green gametophyte. It lacks the true roots, stem and leaves. The gametophytic generation is represented by a dominant, long lived. The gametophyte is of two types that is thalloid and leafy gametophyte. Thalloid gametophyte: The thalloid gametophye lacks the true roots, stems and leaves. The gametophyte is prostrate on ground. It is attached to substratum by delicate hair like structure called rhizoids.

3. These rhizoids are helpful in the absorption of water and minerals. Thalloid gametophyte bears small scale like structures on ventral surface (Liverworts). Leafy gametophyte: The leafy gametophyte shows roots like rhizoids, foliose with stem like axis and leaf like appendages (Mosses). S porophytic generation is short lived. It is dependent on gametophytic generation. Sporophytic generation is more concerned with asesual reproduction and formation of spores. Internal morphology: The internal tissue is homogenous or differentiated parenchymatous .

4. In liverworts, it is sometimes differentiated into photosynthetic and storage regions with air chambers which contains chloroplast. In mosses, there may be axile cylindrical structure that surrounds parenchymatous cortical cells. Reproduction in bryophytes: Bryophytes reproduces by vegetatively and sexually. Vegetative reproduction: It takes place by the fragmentation, adventitious branches, tubers ( Riccia ) gemma bodies ( Marchantia ). Sexual reproduction: The sexual reproduction in bryophytes is of oogamous type. The male sex organ is called antheridium and female sex organ is known as archegonium .

5. The male sex organ antheridium is a multicellular, globose or club shaped body, shortly stalked with multicellular protective jacket. Antheridium contains many androcyte mother cells which gives rise to biflagellate, haploid male gametes called antherozoids . The female sex organ archegonium is multicellular, flask shaped body. They have swollen base portion called venter and narrow distal portion known as neck. The neck portion shows 4-6 neck canal cells. The venter contains non motile large female gamate called egg or oospore. 4-6 venter canal cells Fertilization: The fertilization takes place in presence of water.

6. The fertilization results in the formation of diploid zygote. Embryo: The zygote undergo repeated divisions to form undifferentiated, multicellular structure called embryo. The first division of zygote is transverse and the apex of the embryo develops from upper cell such embryo is called exosporic . The venter wall enlarges with developing embryo to form protective, multicellular envelope called calyptra. By the further divisions and differentiation the embryo produces a small spore producing structure called sporogonium . The sporogonium producing plant body is called as sporophyte. Sporophyte: The sporophyte is simpler than gametophyte and dependent partially or wholly on gametophyte for its nutrition.

7. The sporophyte is mainly concerned with the formation of spores. The sporogonium is divided into abortive foot, elongated seta and spore producing capsule. In higher bryophytes like mosses sporophyte has distinct foot, seta and capsule which are jacketed. The spores are produced by meiosis of spore mother cells in the capsule. The capsule is concerned with the production of wind disseminated, non-motile, cutinized spores which belongs to the category of meiospores . The spores are haploid and similar morphologically. Hence the bryophytes are homosporous .

8. Spore germination and protonema : In favorable conditions each haploid spore germinate to give rise to gametophyte plant either directly ( thalloid ) or indirectly as bud from protonema (Mosses). The life cycle of bryophytes is completed into two generations i.e. gametophytic and sporophytic generation which regularly alternate with each other. These two generations are different from each other in case of morphology, reproduction and nutrition. Such type of generations is called heterologous type of alternation of generation which is a constant feature of the life cycle of bryophytes.

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