Mosses are a group of
small, non-vascular plants that belong to the division Bryophyta. They are
typically found in damp or shady habitats and have a gametophyte-dominated life
cycle. Mosses lack true roots, stems, and leaves, and instead have simple,
leaf-like structures called phyllids that are arranged in a stem-like structure
called a sporophyte. Mosses reproduce via spores and have an important role in
their environment by preventing soil erosion, providing food for animals, and
serving as indicators of environmental conditions.
There are about 12,000
species of mosses. The body of the moss is usually a leafy shoot although some
are secondarily flattened. A moss usually lives in dense colonies or beds.
Mosses can be found from the Arctic through the tropics to parts of the Antarctic.
Although most prefer
damp shaded locations in the temperate zone, some survive in deserts and other
inhabits bogs and streams. In forests, they frequently form a mat which covers
the ground and rotting logs. Mosses can store large quantities of water in their
cells. But if a dry spell continues for long, they become dormant. The whole
plant shrivels, turns brown and looks completely dead. As soon as it rains,
however, the plant becomes green and resumes metabolic activity.
Some mosses are adapted
to unusual conditions. The so called copper mosses live only in the vicinity of
copper and can serve as an indicator plant for copper deposits. Luminous moss,
which glows with a golden green light, is found in caves, under the roots of
trees and other dimly lit places. Its cells, shaped like tiny lenses, focus
(what little light is there) on the grana of chloroplast.
The plant body or
gametophyte is an upright stem-like structure that bears leaf like blades. The
plants may be creeping.
Each individual plant
has tiny root like structures called rhizoids that anchor it to the soil. Moss
sporophytes are often yellowish or brownish at maturity, bear a sporangium or
capsule near their tip, and are borne individually on the gametophyte. Because
the mosses lack specialized vascular tissues, therefore, do not possess true
roots, stem and leaves.
Life Cycle of Moss
The moss plants show
two generations the sporophyte and the gametophyte, which regularly alternate
with each other. It is known as alternation of generation. The life history is
completed when the plant passes through these two generations.
Gametophyte:
The matured green shoot is the gametophyte. It produces gametes and reproduces
by sexual method. The sex organ is at the apex of the shoot. The male sex organ
is known as antheridium and the female sex organ as archegonium. The sex organs
are intermixed with some multicellular hair like structures, known as
paraphyses. The two sex organs may occur on the same plant i.e. monoecious or
on two separate plants i.e. dioecious.
Sporophyte:
The sporophyte consists of a foot which is embedded in the tissue of the
gametophyte and a stalk with a sporangium of the upper end.
Life
Cycle: Spores are formed in the sporophyte by meiosis thus
the spores are haploid. The spore germinates into alga like structure called
protonema, having bud and branches.
The bud gives rise to
gametophyte. In the antheridium the sperms are produced. In the archegonium the
egg is produced. The flagellated sperms swim through the film of water to the
egg. Fertilization is internal. The diploid zygote divides and forms the
embryo. The embryo develops into a
diploid sporophyte.
Mosses play an
important role in their environment. They hold the soil in place and help
prevent erosion. They provide food for animals, especially birds and small
mammals. Commercially the most important mosses are the peat mosses. Their
leaves hold water and are beneficial s a soil conditioner. When added to sandy
soils peat moss helps to hold and retain moisture.
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| Mosses |
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| Moss Life Cycle |
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