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Plant Biology - Stem System

Stem system:
The aerial part of the plant which develops from the plumule is called stem. It is opposite to root system and having negatively geotropic, positively phototropic and negatively hydrotropic.

Section of stem:

1.  Node – develops leaves
2.  Internodes – region between two nodes and combine the node with each other.
3.  Apical bud – present at the tip of stem and helps in growth of stem
4.  Axillary bud – present at the axil of leaf which connects leaf with stem and helps in branching of stem.

Branching of stem:
With the growth of stem, it is divided into different branches to perform various functions. Branching of stem is of two types.
1.  Dichotomous branching: Two branches is developed form apical bud.
2.  Lateral branching: Racemose and Cymose are the two types of branches developed form the lateral sides of stem.
A.  Racemose branching develops from the axillary bud in an acropetal fashion and the shape of the plant becomes either conical or a pyramidal.
B.  Cymose branching too develops from the axillary bud but not in an acropetal fashion.
1.  Uniparous cymose branching - only single branch develops and divided into helicoids and scorpioid cymose branching.
Helicoid develops only on one side, either on right or left, e.g. Ashoka
  Scorpioid develops on both the side, e.g. Vitis
2.  Biparous Cymose branching: Two branches develops, e.g. Carissa
3.  Multiparous Cymose branching: Multiple branches develops, e.g. Red oleander

Types of Stem:
1.  Aerial stem: Mostly strong, erect and woody in nature, however, sometimes it is weak, delicate and threadlike.
2.  Underground stem: Present under the soil and do not contain chlorophyll.

Function of Stem:
1.  Develops leaves and arrange them in proper way so that each leaf can get sufficient sun light.
2.  Transport water and minerals absorb by root.
3.  Transport food to every part of the plant.
4.  Fruits, flowers and seeds arranged in such a way that fertilization and pollination occurs in a proper way.
5.  Underground stems are modified to store foods and are called rhizomes, e.g. Ginger, Turmeric.
6.  Arial stems are modified for vegetative propagation e.g. Pistia, strawberry etc.
7.  Stem develops sharp and pointed structure called thorn for protection, e.g. Rose
8.  Stems are modified into thread like structure called stem tendrils which helps in climbing of the plant around the support system, e.g. Bittergourd
9.  Stems carries photosynthesis are called phylloclades, e. g. opuntia
10.  Axiliary buds and floral buds of the stem stores food and reproduce new plants, such modification is called bulbil, e.g. Agave


Self study:
Q-1: Match the following
A B
Rhizomes Climbing
Thorn Photosynthesis
Stem tendrils Protection
Phylloclades Storage of food

Answer:
A B
Rhizomes Storage of food
Thorn Protection
Stem tendrils Climbing
Phylloclades Photosynthesis

Q-2: Which of the following is not a part of cymose branching?
  1. Helicoid
  2. Scorpioid
  3. Racemose
  4. Uniparous
Answer: Racemose is a separate part of branching which differs from Cymose by its acropetal fashion of branching.

Q-3: Leaves are developed form the …………..of the stem

  1. Node
  2. Internode
  3. Plumule
  4. Axial bud
Answer: Leaves are developed form the nodes of the stem.
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