Get complete information on the Structure of Bryophytes

ADVERTISEMENTS:

The main plant is gametophyte. It is green thallus as in Riccia and Marchantia or it may be differentiated into rhizoids, stem like structure and leaf like structure e.g. Funaria. Both the types of gametophyte are attached to substratum with the help of rhizoids which may be unicellular or multicellular and also function for absorption of water and minerals.

These plants lack vascular tissues. The length of the plants vary from several mms to several cms. The largest plant of the group is Dawsonia which is approximately 40-50 cm long. All cells of gametophyte except rhizoids have chloroplasts due to which they are photoautotrophic. The sporophyte of moss, Funaria is divided into foot, seta & capsule.

Capsule is again divided into Apophysis-the basal sterile region, theca-the central fertile region and operculum-the upper region of capsule is enclosing peristome.

ADVERTISEMENTS:

Reproduction in Bryophytes:

It is of two types:

(A) Vegetative Reproduction:

The gametophyte reproduces by fragmentation, by gemmae, by tubers, by protonema and by bulbils.

ADVERTISEMENTS:

(i) Fragmentation of primary protonema:

Protonema formed by germination of spores is called primary protonema. In the protonema, some cells here and there die, due to which small fragments are produced. If a fragment of protonema has a bud of leafy gametophyte, it develops into an adult plant.

(ii) By secondary protonema:

From any portion of adult leafy plant, e.g. ‘leaf, ‘stem’, ‘rhizoid’, some cells produce a protonema. This is called secondary protonema. Leafy buds arise here and their and are capable of giving rise to new adult plants.

ADVERTISEMENTS:

(iii) By Bulbils:

Bulbils are resting buds produced on rhizoids or protonema. They get detached from the parent plant and under favourable conditions give rise to new plants.

(iv) By Gemma:

From the apical region of ‘leaves’ or axis, small gemma are produced which after being detached from parent give rise to new plant.

ADVERTISEMENTS:

(v) Apospory:

Some cells from any part of sporophyte separate from the parent, fall on the soil and form a protonema. Buds of leafy gametophore are produced on protonema and give rise to a gametophyte like plant but the cells have diploid set of chromosome (2n). In this way a gametophyte like plant is produced from sporophyte without reduction division.

(B) Sexual Reproduction:

Sexual reproduction is oogamous. The biciliate antherozoids are borne in antheridia and oospheres (= eggs) are borne in archegonia, which are flask shaped structures differentiated into stalk, venter and neck.

ADVERTISEMENTS:

Water is essential for fertilization. Oospore (zygotes) are produced as a result of fusion of male and female gametes. Oospore gives rise to the sporophytic generations, called sporogonium. Sporogonium is completely (as in Riccia) or partially (as in Moss) dependent upon gametophyte.

Sporophyte may be very simple and represented by a spore sac only as in Riccia or differentiated into foot, seta and capsule as in Moss. In the spore sacs are borne spore mother cells which after reduction division give rise to haploid spores. All bryophytes are homosporous. Usually the spore germinates to produce a protonema which later on develops into an adult gametophyte. All bryophytes show alternation of generation.

Division 3 Pteridophyta:

Pteridophytes are vascular cryptogams i.e., plant of this group possess vascular tissues (i.e xylem and pholem) for the conduction of water, minerals and for translocation of foods. They are mostly herbacious and grow in moist and shady places. Some important characteristics of pteridophyte are:

(i) The main plant body is sporophyte, usually differentiated into roots (except Psilophyta), stems and leaves (sometimes leaves absent).

(ii) Vascular tissue is differentiated into xylem & phloem.

(iii) In xylem, trachea (vessels) is absent and in phloems companion cells are absent.

(iv) They are flowerless plants.

(v) They do not produce seeds.

(vi) Spores are borne in sporangia.

(vii) Sporangia are produced in groups (sori) on sporophylls.

(viii) The gametophytic plant is smaller and less differentiated (i.e. simple).

(ix) The gametophyte bears male reproductive structure called antheridium and female reproductive structures called archegonia.

(x) The antheridia bears antherozoids and archegonia bears oosphere (egg).

(xi) There is no secondary growth.

(xii) The zygote produces a distinct embryo stage.

(xiii) Distinct alternation of generation is present with the sporophyte as the conspicuous plant in the life cycle.

(xiv) The division contains nearly 10,000 species which is further divided into :

Class 1 Filicineae

Class 2 Lycopodineae

Class 3 Equisetineae.

(xv) Various kind of stele is seen in Pteridophyta.

Web Analytics
Kata Mutiara Kata Kata Mutiara Kata Kata Lucu Kata Mutiara Makanan Sehat Resep Masakan Kata Motivasi obat perangsang wanita