Mosses
belong to the division Bryophyta and the class, musci. Mosses are land plants
which grow on moist ground under the shade of big trees as epiphytes; on packed
wet blocks, and or old block walls and rocks.
Funaria (a common moss species) grows in turfs to form a green carpet. Sometimes, relatively extensive areas may be completely covered by it, particularly the sites of old bonfires in woodlands.
The moss is often able to colonise such
burnt patches remarkably quickly. This is an indication of its measure of
success as a land plant.
Mosses
lack true roots, stems and leaves; they are parenchymatous (i.e. they have
parenchyma tissues), they lack vascular tissue. The gametophyte (the haploid,
gamete producing phase of the plant) is dominant and nutritionally independent,
whereas the sporophyte (the diploid, sporeproducing phase of the plant) is
permanently attached to the gametophyte.
The
mature gametophyte is usually erect and radially arranged. The spores are
released from the sporophyte by a tranverse splitting of the sporangium or
capsule. Mosses play an important role in nature.
Characteristics of Mosses
Do
you remember that living organisms have some characteristics or features that
are peculiar to them? Mosses as living organism have their peculiar
characteristics.
The
following characteristic features of mosses below:
1.
The plant is small and erect.
2.
Persisting vegetative body is attached to subsratum.
3.
Body consists of attaching and absorbing rhizoids and, aerial part for
photosynthesis.
4.
Dichotomous branching. Growth is from a single cell or row of cells.
5.
Low degree of tissue differentiation.
6.
Well defined sexual reproduction.
7.
Sex organs are the antheridia and archegonia.
8.
Fertilization is with biflagellate male gametes.
7.
Plant body is one haploid gametophyte.
8.
Diploid sporophyte (sporogonium) is partially or wholly dependent upon the
gametophyte.
9.
Spores are of one type (homosporous) Spores usually germinate into an
intermediate structure (protonema). Mainly terrestrial but in wet environment.
10.
Commonly found on old damp walls, tree trunks and wet ground. They are
gregarous, forming green carpet.
11.
Small in size measuring a little more than one centimeter in height.
12.
Axis is short with spiral, minute green leaves. True roots are absent but
rhizoids are present for absorption and anchorage.
13.
Rhizoids are made of cells not differentiated into tissues and organs. The stem
(no conducting tissues) is short, slender and often with a branching stem,
covered by remains of archegonia rosette of leaves neck at tip of male shoot
cluster of leaves at tip of female shoot; surround archegonia (female sex
organ) 'leaf' - well developed with conspicuous midrib; leaves spirally
arranged 'stem capsule - photosynthetic; green when immature, orange-brown when
ripe annulus - cells here force off operculum when capsule is ripe operculum -
lid of capsule sporophyte semi-dependent on gametophyte Access Biology simple leaves spirally arranged
along the stem and its branch.
The two branches of stem are differentiated into male and female branches.
The sporogonium consists of a long seta (stalk) and a pear-shaped capsule.
The rhizoid, stem and leaves all together form the gametophyte.
The gametophyte
alternates with the sporophyte during the life cycle. This is called
alternation of generations.
Reproduction in Moss
You
will find reproduction in moss very interesting. Would you like to know how
reproduction occurs in moss plant? The moss plant (e.g. Funaria) bears separate
male and female parts at maturity, biciliate spermatozoa (antherozoids) and
large ovoid eggs are formed at the top of the plants.
Reproduction
takes place in the rainy season as male gametes swim in water into the
archegonium (multicellular structure in which an egg is produced, a female
gametangium).
Male
gametes (antherozoids) are released by the male plants after rainfall when
water covers the top of the plants growing in turfts.
Male
gametes (antherozoids) swim in water into the archegonium on the female plant
within the tufts. One antherozoid fuses with one egg in the archegonium of the
top of a female plant. A zygote is formed on the top of the female plant.
The,
zygote develops into a sporogonium which constitutes the sporophytic
generation. This is the spore-producing structure which is partly dependent on
the gamete producing structure for its nourishment.
The
bryophytes (moss and liverworts) have two phases in their life history
1.
The gametophyte phase which reproduces sexually by means of gametes
2.
The sporophyte phase which reproduces asexually by means of spores
This
phenomenon is known as the Alternation of Generations. It is very necessary for
you to know more about the Antheridium, Archegonium, gametophyte, sporophyte
and Alternation of generations and the roles they play in the development of a
new moss plant.
The Antheridium
It
is club-shaped. Inside are antherozoid mother cells (or androcytes) a mass of
small cells surrounded by a simple layer of cells that form the wall or jacket.
Each develops into a single antherizoid. Antheridium lid opens to liberate
antherizoids. Antherizoids are minute, spirally coiled and bicilliate. They
swim in films of water to the archegonium.
The Archegonium
It
is flask-shaped. Consists of swollen portion (venter) and upper tube-like neck.
Neck canal secretes mucilage and malic acid to attract antherizoids
Fertilisation occurs in the venter to form zygote Zygote secretes thick walls
to become oospore. Oospore germinates through the apex to form the sporogonium
(sporophyte).
The Gametophyte
Bears
reproductive organs. Male organs: the antheridium produces antherizoids. The
female organ, the archegonium, borne on separate shoots/branches produces egg
cell or ova. Both are protected by hair-like structures called paraphyses.
Read On: Algae: Characteristics, Classification, Reproduction and Importance
•
The sporophyte produces spores.
•
Consists of foot, seta and capsule.
•
Capsule dehisces, spores are liberated and dispersed.
•
Spores germinate.
•
Under favourable conditions, spores germinate into short tube which forms a
green muchbranched filament called protonema.
•
Develop slender-brown rhizoids and small lateral buds.
•
Buds develop into new moss plants.
Alternation of Generations
•
Funaria shows two stages in its life cycle.
•
The growing plant is the gametophyte.
•
Sporogonium is the sporophyte.
•
Fertilization leads to formation of sporophyte.
•
By asexual production of spores, gametophyte germinates.
•
Chromosomes are reduced to haploid number during spore formation.
•
There is thus an alternation between the gametophyte and sporophyte phases.
Economic Importance of Mosses
Let
us now consider the economic importance of mosses
1.
Mosses grow and reproduce rapidly on a favourable substrate and under
favourable environmental conditions. As they die and decompose, they form
suitable humus on which other higher plants can grow. They, therefore, form a
necessary step in the natural process of ecological succession that may lead to
climax vegetation.
2.
The bog or peat moss (sphagnum) actually consists of a mixture of plants of
which the sphagnum forms the dominant vegetation. This plant colonises an acid
environment. The plant, itself, has antiseptic properties for which reason it
does not decay fast.
Thus,
the plant debris accumulates as "peat" Peat is often dried and used
as fuel. It is also useful in agriculture because of its water-holding capacity
for which it is frequently mixed with sandy or humus-poor soils. There are
reports that sphagnum has been sterilised and used for wound- dressing because
of its waterholding characteristics.
Fungi: Classification, Characteristic, Structure, Reproduction and Facts
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