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PinkMonkey Online Study Guide-Biology
BRYOPHYTA
These are terrestrial non-vascular plants which still
require moist environment to complete their life-cycle, hence they are
called amphibians of the plant kingdom. Bryophytes show advances
over alga by developing special sex organs like antheridia (male)
and archegonia (female) and show distinct alternation of generations.
Bryophyta are the simplest of land plants, and include mosses, liverworts
and hornworts.
They are distinguished by the following characteristics:
(1) They are small terrestrial plants.
(2) They are without a distinct root system but attached to substratum by rhizoids.
(3) They do not posses true vascular tissue.
(4) Sex organs are multicellular with a protective jacket layer.
(5) Gametophyte is dominant and independent.
(6) Sporophyte is small and parasitic or semiparasitic on the gametophyte.
(7) They show a distinct alternation of generations.
Bryophytes are divided into three classes
Class : Hepaticeae : These are lower forms with
an undifferentiated thallus, Rhizoids are unicellular and unbranched,
Protonema are absent. Sporophyte is short-lived and simple. However, in
some forms it may be differentiated into foot, seta and capsule. Examples
are Riccia, Marchantia.
Class : Anthocerotae : Gametophyte is undifferentiated
thallus, rhizoids are unicellular and unbranched. Protonema is absent.
Sporophyte is differentiated into foot and capsule only. An example is
Anthoceros.
Class : Musci : These are higher forms in which
the gametophyte is differentiated into stem-like and leaf-like parts showing
radical symmetry. Rhizoids are multicellular and branched. Protonema present.
Sporophyte is differentiated into foot, seta and capsule. An example is
Funaria.
External Morphology : Since bryophytes lack efficient conducting tissue, they do not become very large. They are small plants forming green velvety patches on moist substratum. They are green due to presence of chloroplasts. The plant body is either thallus or distinguished into stem-like and leaf-like structures. They are attached to the substratum by rhizoids.
Liverworts
Figure 14.34 Types of bryophytes
The plant body is a thallus which is a gametophyte. It
is dorsoventrally flat, showing dichotomous branching. The dorsal surface
is marked by a groove throughout, while the ventral surface shows unicellular
rhizoids. Reproduction takes place vegetatively, asexually as well as
sexually. Vegetative reproduction takes place by production of vegetative
reproductive bodies called gemmae. The gemmae eventually separate
from the parent plant and grow into gametophytes. Sexual reproduction
takes place by producing antheridia and archegonia which
may be on erect branches called antheridiophores and archegoniophores.
The antheridia produce biflagellate antherozoids. In presence of water
they reach the archegonium, enter the neck and only one fertilizes the
egg at the base, to form a diploid zygote developing into asporophyte.
The sporophyte remains attached to the gametophyte. Asexual reproduction
takes place by production of haploid spores which are produced by the
sporophyte. The spore germinates to produce a gametophyte, thus showing
alternation of generations.
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