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.
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| Mosses |
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.
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Life cycle of moss
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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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