Dicot stems have a well-defined layer of epidermis and internal structures such as pith, pericycle, hypodermis, cortex and endodermis. Here, let’s learn about the primary structure of the dicot stem in detail.
Table of Contents
- Epidermis
- Hypodermis
- General cortex
- Endodermis
- Pericycle
- Vascular bundle
- Medullary rays
- Pith
- Frequently Asked Questions
Epidermis
The epidermis is the stem’s outermost layer. It is made up of tightly packed elongated, parenchymatous cells that show up as rectangular structures in transverse sections. The cells lack chloroplasts and are transparent. They have an outer layer of cuticle and an inner layer of the protective epidermis. The epidermis also has several trichomes or multicellular hairs that cover the cuticle.
The epidermis contains tiny pores known as stomata in certain locations that aid in gas exchange. Each stoma has a pair of guard cells, which are specialised kidney-shaped cells that contain chloroplast. They regulate the closing and opening of stomata.
Hypodermis
Three to four layers of subepidermal collenchyma tissue make up the hypodermis. The collenchyma fibres that make up the hypodermis are frequently green in colour. Below the stomata, the hypodermis is either nonexistent or barely visible.
General Cortex
General cortex is made up of parenchymatous cells. They enclose the gaps between cells. The outer cortical cells of the juvenile green stem have chloroplasts (chlorenchyma) and produce food. However, the cortex’s primary job is to store food.
In dicots like sunflowers, there are several longitudinally running oil ducts that go through the cortex and each oil duct has a channel that is bordered by a tiny glandular cell epithelium.
Endodermis
It is a one-cell thick, wave-like layer. The endodermis is located at the innermost edge of the cortex. It is composed of cells with a barrel shape that do not encapsulate intercellular gaps. Typically, Casparian strips are absent.
As a food store, the endodermal cells frequently have noticeable starch granules. Thus, the stem endodermis is also called a starch sheath.
Pericycle
The pericycle is a thick, layered tissue. It is outside the vascular strand and is located inside the endodermis. It is heterogeneous in nature. Parenchyma and sclerenchyma fibres both make up its structure. Sclerenchyma appears as semilunar or semicircular patches called bundle caps. The sclerenchymatous pericycle, also referred to as hard bast, is the bundle cap that is connected to the vascular bundles’ phloem, whereas the parenchymatous pericycle is located outside the medullary rays.
Vascular Bundle
The vascular strand is found as an inner ring of vascular bundles or eustele that surrounds the central pith of the pericycle. The number of vascular bundles is always definite. The phloem (primary) is located on the outside of each vascular bundle, the xylem is on the inside and a cambium strip is in the middle.
Xylem
Xylem can be discovered near the pith or inner part of the vascular bundles. Tracheids, vessels, xylem parenchyma and xylem fibres make up the xylem. Here, only the xylem parenchyma cells are considered as living cells. Their primary role is to act as water-conducting tissues.
Phloem
It is located on the outside of the vascular bundle, close to the pericycle. Sieve tubes, companion cells, phloem parenchyma and some phloem fibres make up phloem. They play a complicated role in moving soluble organic food substances.
Cambium
A vascular bundle’s cambium is a thin band of primary meristematic cells that lies between the phloem and the xylem. It is also called fascicular cambium and intrafascicular cambium.
Explore: Preparation and Study of T.S. of Monocot and Dicot Roots and Stems
Medullary Rays
The cortex, pericycle and pith are linked by the medullary rays. The cells of the medullary rays are more substantial than cortical cells. The ray cells are polygonal in shape.
The intercellular gaps are very small. Through pits, ray cells come into close touch with the phloem and xylem’s conducting cells. Food and water are transported radially with the aid of medullary rays. Additionally, they move gases from the cortex to the pith and vice versa.
Pith
It serves as the stem’s centre. Polygonal oval or spherical parenchyma cells that encapsulate intercellular gaps make up the pith. The food is stored by the pith cells. In some dicots, such as Cucurbita, the middle portion of the pith separates to form a cavity (pith cavity).
Keep exploring BYJU’S Biology to learn more such exciting topics.
See More:
- Difference between Monocot and Dicot Stem
- Difference between Dicot and Monocot Root
- Monocot and Dicot Plants Anatomy
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