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  Bryohytes, Biology tutorial

Introduction to Bryohytes:

In course of evolution, the modification from aquatic habitat to terrestrial habitat happened and only ancient land plants developed. These are called as bryophytes. Though bryophytes colonize terrestrial habitats however they are dependent on water for completion of the life cycle. They create motile male gametes that need the thin film of water for the motility to reach non-motile female gamete to achieve fertilization.

General Characteristics of Bryophytes:

Bryophytes lack roots and don't have vascular system. Few mosses include the primitive system of tubes which perform water and food - conducting tubes are known as leptoids. The single plant is very small, barely a few cm in size. It hardly ever develops large because of lack of supporting tissues. Bryophytes illustrate 2 distinct and well distinct stages of life cycle, sexual and asexual that follows each other. Gametophyte is haploid and develops gametes. Sporophytes are diploid and produces spore. Haploid generation alternates with diploid genetic called as Alternation of generation. Gametophyte may be thalloid or has the axis differential in stem-like and leaf-like structures that have xylem and phloem. Gametophyte is green, photosynthetic and nutritionally independent, and attaches to soil by unicellular or multicellular filaments known as rhizoids. Rhizoids show like roots but they do not have vascular tissues.

Bryophytes are more plentiful in moist tropical areas. They also produce in deserts, mountains. In dry areas, the growth and activity is limited to wet season only.

Morphology of Bryophytes:

Bryophyte is mainly divided in liverworts and mosses.

Liverworts:

Gametophytes generally are close to ground. There are two types of liverworts namely; thalloid liverworts (gametophyte) and dorsi-ventral, with upper and lower surfaces. Leafy liverworts (distinguished in leaf-like and stem-like structures). Leaves of liverworts are with no midribs. Grows on moist ground or rocks which are also wet. (Can be situated in muddy areas. Examples comprise Marchantia and Riccia.

Mosses:

This is largest class of Bryophytes. They are split into 3 subclasses: Sphagnidae (Reat mosses) Andreaide rock mosses) and Bryidae (true mosses). Example comprises funaria.

External Features of Marchantia:

i) Marchantia (Liverwort) Marchantia belongs to family marchantiaceae. Gametophyte bears archegonia on vertical stalked receptacles known as archegoniophore. It develops in cool moist places together with mosses and increases of burnt grounds. It is deep green in color has the important midrib that is marked on dorsal surface by the shallow groove and in ventral surface by the low ridge covered with rhizoids. Marchantia is decorous. Thallus of Marchantia is attached to surface by rhizoids that are of smooth walled. Scales are also present on ventral surface arranged on both side of mid-rib.

External Characteristics of Funaria (Mosses):

i) Funaria is very common moss and extensively distributed throughout world. Adult gametophyte is most conspicuous form of moist plant. It comprises of the main erect axis bearing leaves that are arranged spirally. Adult gametophyte is known as gametophine. It is small and approx 1-3 cm high. Leaves don't have stalk but illustrate the distinct midrib.

ii) The gametophore is joined to substratum by rhizoids. They are multicellular, branched and contain oblique septae. The gametophyte bears sporophyte that includes foot, seta and capsule. Gametophore grows from the filamentous, green short-lived protomenue.

Adaptation of Bryophytes:

i) Bryophytes are set to soil through thread-like, small structures known as Rhizoids. Rhizoids are unicellular and unbranched in liverworts however multicellular and branched in mosses. They join plant to soil and absorb water and minerals from it.

ii) Hydroids transfer water from rhizoids to leaves at apex and food conducting leptoids transport sucrose. In most other bryophytes, exterior capillary system takes care of distribution of water to all parts of plant body.

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