Question

Explain internal structure of dicot stem in detail with a neat labelled diagram.

Answer 1

The transverse section of a dicot stem reveals the following structures.
1. Epidermis:
It is the outermost layer. It is made up of single layer of parenchyma cells, its outer wall is covered with cuticle. It is protective in function.
2. Cortex:-
It is divided into three regions:
(i) Hypodermis: It consists of 3 - 6 layers of collenchyma cells. It gives mechanical support.
(ii) Middle cortex: It is made up of few layers of chlorenchyma cells. It is involed in photosynthesis due to the presence of chloroplast.
(iii) Inner cortex: It is made up of few layers of parenchyma cells. It helps in gaseous exchange and stores food materials.

• Endodermis is the inner most layer of cortex it consists of a single layer of barrel shaped cells, these cells contain starch grains. So it is also called starch sheath.

3. Stele:
The central part of the stem inner to endodermis is known as stele. It consists of pericycle, vascular bundle and pith.
(i) Pericycle: It occurs between vascular bundle and endodermis. It is multilayered, parenchymatous with alternating patches of sclerenchyma.
(ii) Bundle Cap: There is a patch of hard sclerenchyma tissue outside to the phloem of vascular bundle is calld Bundle Cap.
(iii) Vascular bundle: Vascular bundles are conjoint, collateral, endarch and open. They are arranged in the form of a ring around the pith.
(iv) Pith: The large central parenchymatous zone with intercellular spaces is called pith. It helps in the storage of food materials.
Transverse section of a dicot stem