which parts are absent in monocot stem
Answers
Answer:
Explanation:
Internal structure of monocot stem
1. Epidermis Epidermis is the outermost covering of the stem represented by a single layer of compactly arranged, barrel-shaped parenchyma cells. Intercellular spaces are absent. Trichomes are absent. A cuticle is present. The epidermis contains numerous minute openings called stomata.
2. Hypodermis Hypodermis is a region that lies immediately below the epidermis. It is represented by a few layers of compactly arranged sclerenchyma cells.
3. Ground Tissue Ground tissue is a major component of the stem. It is undifferentiated. The ground tissue is represented by several layers of loosely arranged parenchyma cells enclosing prominent intercellular spaces. The ground tissue is meant for storage of food.
4. Vascular Bundles They are found irregularly scattered in the ground tissue. Towards the periphery, the bundles are smaller in size while towards the centre, they are larger in size. The smaller bundles are younger, while the larger ones are older. Hence, the arrangement is described as centrifugal. Each vascular bundle has a covering called bundle sheath formed by a single layer of sclerenchyma cells. The vascular bundle encloses both xylem and phloem.
5. Vascular Bundles Xylem is found towards the inner surface and phloem towards the outer surface. Cambium is absent. Hence the vascular bundles are described as conjoint, collateral and closed. In the xylem, there are two metaxylem and two protoxylem vessels arranged in 'the shape of 'Y'. The lower protoxylem vessel is non functional and remains as a water filled cavity called lisigenous cavity or protoxylem cavity. Xylem is described as endarch. In the phloem, only sieve tubes, companion cells and phloem fibres are present. Phloem parenchyma is absent.
6. * Absence of trichomes. * Presence of stomata. * Presence of a hypodermis made up of sclerenchyma. * Presence of undifferentiated ground tissue. * Presence of numerous vascular bundles irregularly scattered with cerifugal arrangement. * Vascular bundles are conjoint, collateral & closed with endarch xylem. * Presence of only two protoxylem & two metaxylem vessels in each bundle. * Presence of a lysigenous cavity. * Absence of phloem parenchyma. * Presence of a bundle sheath made up of sclerenchyma.
In monocot stem, epidermis, hypodermis, ground tissue, and vascular bundles are present. General cortex, endodermis, pericycle, medulla, medullary are absent.