Morphology is concerned with external characteristics
while anatomy is concerned with internal characteristics.
Stem is negatively geotropic and positively phototropic
i.e. it grows away from the earth and towards light. Young
stems are green in colour and help in photosynthesis. Mature
stems are generally brown and they have nodes and internodes.
From the nodes axillary buds develop which then becomes
a new stem
There are three types of buds-
1. Terminal (apical)
Axillary is present on the axil of the leaf i.e. between
the stem and the leaf. From the axillary buds branches arise.
Sometimes from axillary buds instead of branches flower
also arise then these buds are called floral buds. The distance
between two adjacent nodes is called internode. The slight
swelling from where the axillary buds and leaves originate
is called node. If nodes are present clearly they cam be
easily identified. In mature stems nodes are not easily
identified. Stems support the remaining part of the shoot.
It transports water and minerals from roots to leaves and
prepared food from leaves to all parts of the plant.
Plants will grow internally but they are not able to grow
externally at the same time. Hence cracks are developed
as it cannot hold the structure. This happens in dicot plants
because in monocot plants there is no external growth. Through
these gaps exchange of gases will take place. They are called
Stomata are mall pores present on the surface of leaves
and stems (immature). They are guarded by guard cells which
contain chlorophyll. Stomata opens during the day and closes
during the night by the help of guard cells. Branches can
be differentiated into nodes and internodes because of leaves.
Chloroplasts identify the presence of light. Stem ,roots
and leaves are the vegetative parts of the plant. Stem is
modified for additional functions also.
Stem is modified for food storage.
Tuber -. There are some underground stem
which swell up and the swell up structure is called stem
tuber. If we analyze it then we find that it contains several
eyes. Scale leaves and axillary buds together form the eyes
of the potato. Eyes are protected by scale leaves eyes can
be used as a means of vegetative reproduction. Seed are
not used as they have less food and those plants which grow
are weak. To provide with strong plants we use eyes. Depressions
are nodes e.g. potato.
Rhizome - it grows horizontally and underground
to the surface of soil. It has regular nodes and internodes.
The nodes and internodes are protected by scale leaves.
In the axil of the scale leaves axillary buds are present
Corm - it grows vertically to the surface
of the soil i.e. downwards. They are swollen up structures
axillary buds are present but they are not arranged properly
i.e. internodes are present but not identified. Scale leaves
are there around axillary bud. Contractile roots are present
and they fix into the ground so that the stem will grow
downwards. Axillary buds develop into a new corm. e.g. colocassia.
Bulb- here food is stored in scale leaves.
Leucoplasts store food. Terminal bud or axillary bud develops
into new aerial shoot. e.g. onion.
Sub aerial stem modifications
Here stem is on the surface of the soil and performs additional
function i.e. vegetative propagation.
Runner - branches originate from the main
plant in all directions. From parent plant daughter plants
are produced. After growing for some time with the mother
plant the daughter plant is separated from the mother plant.
In most plants vegetative propagation takes place. Only
the mother plants contain true roots the daughter plants
contain adventitious roots.
Stolon - in comparison to the runner the
stems are thick. They originate from the base of the mother
plant. It grows into the air for some time and it finally
reaches the ground.
Offset - it is generally in aquatic plants. It is a short
and thick stem.
Sucker - they originate from underground
and grow obliquely and reach above the soil. When it comes
up a new plant is formed.
Aerial stem modification
They grow above the soil and perform additional function
and provide support to the plant.
Stem tendril - in some weak plants the
stem modifies and forms a coiled wiry structure and attaches
itself to a hard object. It is used for climbing on hard
objects for support. If the tendril originates from axillary
or terminal bud then it is called stem tendril. If it is
growing from the tip it is called terminal bud. If it is
growing from axil it is called axillary bud.
Twiner - the stem itself turns around
the solid object. There is no thorn or tendril.
Thorns - it is present for protection
from the enemies. Axillary buds are modified into thorns.
Thorns are hard in nature whereas spines are comparatively
soft. Normally spines are developed from the leaves.
Spines are also known as prickles. If
the thorn or the originates from the axillary or terminal
bud then it is called a stem modification. If it is present
just outside the branch then it is called leaf modification.
If it is present on any other part other than the ones mentioned
above then it is called epidermal hairs.
Phyloclade - if the stem does photosynthesis
then it is called a phyloclade. It is flat, green and thick.
It is flat for increasing the surface area, thick for storing
water and green for photosynthesis. In this leaves are modified
into spines to reduce transpiration (evaporation of water
from aerial parts of the plant). Cuticle is an outer covering
which is present for preventing transpiration.
Cladode - stem is modified for photosynthesis.
Therefore it is green in color but thick and short of only
one internode length. Axillary buds are modified into thin
,short and greenish structures. These branch like structures
are called cladode. Leaves are modified into spines. The
function of spines is protection as well as to reduce transpiration.
Bulbil - some auxillary buds or adventitious
buds develop from the plant and store food material and
they detach from the plant and develop into new plants.
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