Plant Kingdome - Bryophytes | NCERT concept | Neet Concept | Biology

 

Plant Kingdome - Bryophytes

BRYOPHYTES

• Bryophytes are most primitive non - vascular terrestrial plants of moist habitats in which a multicellular diploid sporophyte is completely dependent on an independent multicellular haploid gametophyte.
• They are called " amphibians of plant kingdom " because although they are terrestrial plants fundamentally but require presence of water for sexual reproduction .
• Bryophytes are divided into three classes - hepaticopsida ( liverworts ) , anthocerotopsida ( hornworts ) and bryopsida ( mosses ) .
• The dominant phase of the plant is a free living gametophyte .
• The gametophytes are either thalloid ( not differentiated into true roots , stem and leaves ) or leafy shoot having stem - like central axis and leaf - like appendages .
• The vascular tissues are completely absent .
• Rhizoids are present instead of roots which may be unicellular or multicellular .
• Vegetative reproduction occurs through fragmentation , gemmae , e.g. , Marchantia , adventitious branches , e.g. , Riccia .
• Two types of sex organs are present , male antheridium and female archegonium . Both are multicellular and jacketed .
• Antheridium produces a number of flagellate male gametes called sperms or antherozoids .
• Archegonium is flask - shaped with tubular neck and a swollen venter 
• The venter encloses a venter cavity having a sterile venter canal cell and a fertile egg or oosphere .
• An external layer of water is essential for the swimming of male gametes to the archegonia .
• Embryo stage is present . The embryo grows into a sporophyte .
• The sporophyte consists of foot , seta and capsule . 
• Sporophyte produces haploid meiospores inside its capsule .
• Each spore on germination produces a gametophyte , either directly or a juvenile filamentous stage celled protonema ( in case of mosses ) .
• Bryophytes show heteromorphic or heterologous alternation of generations .

Importance of Bryophytes

• Prevention of soil erosion : Mosses form dense mats over the soil and prevent soil erosion by running water .
• Soil formation : They make an important link in ecological succession on rocky areas by taking part in soil formation in rocky crevices , formed by lichens . For example , growth of Sphagnum fills ponds and lakes with soil .
• Water retention : Some bryophytes or mosses can absorb water such as Sphagnum which can retain or absorb 18-26 times water of its weight . This water retention capability is employed by gardeners to keep seedlings and cut plants moist during transportation and propagation .
• Peat : Sphagnum often grows in acidic marshes where there is little decay . The dead parts of moss and other marshy plants slowly get carbonised , compressed and fossilised over thousands of years to produce a dark spongy mass called peat . It is dried , compressed and cut to form blocks . Peat is used as good manure to overcome soil alkalinity and it increases water retention as well as aeration of soil .
• Bryophytes seldom attain great heights and thus remain small in size . It may be due to absence of roots and vascular tissues , absence of cuticle on plant body , absence of mechanical tissues and requirement of external sheet of water for capillary conduction

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