Stem: defination, functions and stem modification | study science

                                                             Stem

Stem definition

The stem is the ascending part of the plant bearing branches, leaves, flowers and fruits.
- It develops from the plumule of embryo of a germinating seed.
- The stem bears node and internodes. The region of the stem where leaves are born called nodes.    Inter-nodes are portion between two nodes.
- stem arrange leaves in a way that it get direct sunlight to perform photosynthesis.
- stem bear buds.
- stem is generally green when young and later often become woody and dark brown.

 

Function of stem

 
1. Stem support the leaves,
2. Conduct water and minerals to the leaves
3. Stem help in storage of food
4. Stem protect the vegetative propagation 

Stem modification

 The stem is the part of the plant that provides support and helps in conduction. Conduction of water and minerals and food.
* In some plants stem is modified for some other function such as
1. Underground stem modification
2. Sub aerial modification
3. Aerial modification

1. Underground stem modification - stem are modified for food storage and to survive under and favourable condition. Some underground stem modification are..

Rhizome - These are non green, brownish in color. Rhizome are fleshy due to storage of food material. e.g. Ginger

Bulb - Fleshy scale leaves are present. Base of bulb consist of cluster of adventitious root. e.g. Onion, garlic

Tuber - It is a fleshy part of the plant which store food. Potato is most common tuber used as food. It does not contain adventitious root.

Corm - This is condensed form of stem. It is spherical in shape. e.g. colocasia

 

2. Sub aerial modification - the stem is partially above the ground and partially below the ground.

*Plants with weak stem that cannot stand upright but spread on the ground are called creepers.

These are modified into..

Runner - It is a creeper. It arise from the auxiliary buds. It break of and grow into independent plant.  e.g. Cynodon

 

 

 

Sucker  - It arise from basal part of main stem. Before separating it develops adventitious root and leafy shoot. e.g. Mentha

Stolon  - Grow aerially for sometime and then downwards to touch the ground. It arise from base of main stem. e.g. Jasmine

 

 

 

Offset - It is shorter and thicker found in aquatic plant. It is a short runner with one internode. e.g. Pistia 

 

3. Aerial Modification- stem are modified into aerial form to perform important functions such as climbing, food storage, vegetative propagation.
Axillary buds are modified to Thorn and tendril for protection and support.
 * Plant those take support and climb up are called climber.

The stem modification are as follows..

 

 

 

Tendrils - It develops from axillary buds. It help plant to climb. e.g. Cucumber, watermelon

Thorns - axillary buds of stem may get modified into woody, straight and pointed thorns. Thorns used as defence organs. It has to check transpiration. e.g. Bouganvillea

• Some plant modify their stem into flattened (cactus) fleshy cylindrical structures (Euphorbia)