Stem - Function and its modification

 

The stem is the aerial part of the stem that bears leaves, flowers and fruits. It develops from the plumule of embryo of germinating seed.

The stem also has two part nodes and internodes. The region from where leaves originated, called nodes. The region between the two nodes is called internode.Stem is soft and green at earlier stages but turns woody and tough at older stages.

It also assumes buds which can be terminal or axillary. Bud is an undeveloped young stem. It has a point that looks like a growing point of leaves or stem branches.

👌👌Remember - Largest bud can be seen in cabbage.

The function of the stem is - It bears leaves, flowers and fruit. It conducts water mineral and food synthesis during photosynthesis.

Modification of stem 

When stem starts to perform different functions other than main functions termed stem modification. During stem modification, it functions like food storage support  protection and vegetative propagation.

Modification of stem in food storage

Stems are modified to perform different functions. Underground stems of potato ginger turmeric jimikand colocasia are modified to store food in them. They also act as organs of perennation to tide over  in unfavorable conditions for the growth.

Tuber is a stem modification of a potato. It also helps in vegertative propagation.

In Ginger and turmeric , rhizome is a modification of the stem. Rhizome grows horizontally below the soil surface. It bears nodes and internodes also.

In colocasia, zaminkand Amorphophallus, the stem modification is called corn which also helps vegetative propagation in addition to storage of food.

Modification of stem in support

Stem tendril is another  modification of ste.It also helps   in climbing with any support like cucumber and grapes.Tendril is spirally coiled and slender in structure. It develops from the axillary buds of the stem.

Modification of stem in defense

In Citrus and Bougainvillea, thorns are developed  from the axillary buds of the stem. Thorn provides protection from browsing animals. In xerophytic conditions or arid areas, some plants like opuntia and Euphorbia stem are modified into fleshy structures called phylloclades. These stems  are modified to perform photosynthesis. The longest part of phylloclades is called cladode which is also capable of photosynthesis.

Modification of stem in vegetative propagation 

In grasses and strawberries, underground stems grow horizontally and form new plants when the older plants die. The parts of plants that grow and form new plants are called runners. 

In some plants like mint and jasmine, a lateral branch is arisen from the main branch of stem. This branch grows aerially for some time and moves downwards to form new plantlets. This is called stolon.

A lateral branch of stem with short internodes bearing nodes with a group of leaves called offset. This is capable of giving rise  to new plants.It can be seen in pistia and Eichhornia.

Sucker is an underground portion which arises from the lateral branch of the stem. It grows initially horizontally under the soil and then emerges from the soil towards the upward and develops leafy shoot in Banana pineapple chrysanthemum.