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STEM
The system which grows aerially in a plant is known as shoot system which develops from the plumule of the embryo and the axis of
this is known as stem.
The branches are developed on the stem either horizontally or
obliquely and the appendages like leaves, bud and flowers are developed on the stem as well
as on the branches.
Ø Characters
·
The stem grows always in +ve phototropic and the –ve
geotropic manner.
·
The stem always grows vertically which is
maintained by the apical bud and it is divided into nodes and internodes,
leaves are developed on the stem at nodes.
·
The axillary buds are developed in the axils
(angle between leafs and stem) which produces branches.
·
Colour – young stems (green), woody stems –
(brown).
·
Generally stem is in the shape of cylindrical
but it is triangular in bilberry,
quadrangular in tulasi and ridged in
pumpkin.
Ø Functions
·
The stem helps in exposing the foliage to
sunlight for efficient photosynthesis.
·
The stem
conducts water and mineral salts absorbed by the roots to the leaves and also
synthesis the food material.
Ø Types
Based on the morphology these are classified
into three types. They are as follows:
·
Herbs
The plants without having woody nature which
can survive for about few years. According to the life span they are of four types as follows
ü Annuals: survive for one year. Example: Rice
ü Biennials: survive for two years. Example: radish
ü Perennials: survive for more than two
years. Example: Day lilies.
ü Ephemerals: survive for few weeks. Example: spring beauties.
·
Shrubs
The plants
which have woody nature but no trunk which develops strong branches at the
ground level and gives bushy appearance.
Example:
Rose
·
Trees
The plants
that shows large wood grows away from the soil at a greater height on stem.
Depending on development of branches they are 3 types as follows:
§ Deliquescent trees
After
producing some branches stem stops its growth then axillary buds produce many
branches and the main stem looks like umbrella.
Example: Banyan
tree.
§ Excurrent trees
Apical
bud grows indefinetly and the main stem grows vertically in racemose manner,
all the branches formed from the axillary buds are arranged aropetally to make
the stem conical.
Example: Eucalyptus
§ Caudex trees
Main
stem remains unbranched, long and short, leaves are arranged at the apex of the
stem.
Example: Coconut
tree.
·
Weak stemmed plants: the plants which grow with
weak stem either horizontally or vertically with the help of support. They are
of 3 types namely
Erect stemmed plants
Prostrate plants
Climbers
Erect
stemmed plants or Culm
Stems
are differentiated into nodes and internodes and the stem looks like a jointed
one which is called as Culm.
ü
Internodes:
Area of a plant stem between two nodes.
Example: sugarcane.
ü
Nodes:
Area of a plant stem from which leaves grows.
Prostrate
plants or trailors
Plants
are fixed in soil at one place which is long, slender stems and branches
present along the surface of the soil in many directions. They are of two types as follows
·
Decumbent
plants: The plants which are fixed in soil at one place with the help of
roots. They consist of vegetative parts which grow horizontally and
reproductive parts which grow vertically.
Example:
Tridax
·
Procumbent
plants: The part of the stem consists of vegetative and reproductive parts
which spread out on the ground.
Example:
Tribulus
·
Climbers:
In this plant grows verticvally with the help of support. They are of 5 types:
ü
Twinners
ü
Tendrils
ü
Root climbers
ü
Stragglers
ü
Lianes
§ Twinners: In some weak stemmed plants
the stem twines around the support and grows up which are known as twinners.
They coil around the support loosely at first and then tights it, depending on
the coiling they are of 2 types as
follows
ü Dextrose: Coils in clockwise direction.
Example: Diascora
ü Sinistrose: Coils in anti-clockwise
direction. Example: Dolichos
§ Tendrils: The weak stemmed plants
produce sensitive and specialized climbing organs which are called as tendrils.
They coil around the support and helps in climbing.
Example: Passifora
§ Root climbers: In some plants the weak
stems produces climbing roots at nodes. They will climb up with the help of
adventitious roots.
Example: Piper
betel
§ Stragglers: The plants which are woody
climbs up with the help of modified organs like hooks and thorns are called as
stragglers.
Example: Bougainvillea
§ Lianes: These are woody twinners, in
the young stages the stem around the support and grow up woody after maturity
stage.
Example: Bauhinia
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