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.