Describe the T.S of a Monocot stem .

Explanation

The structure of monocot stem can be understood well by observing the T.S of stem of Zea mays .It shows 4 distinct parts ., namely 1 . Epidermis , 2. Hypodermis 3. Ground tissue and 4 . Vascular bundles .
(1) Epidermis : It is the outermost layer composed of rectangular or tubular living cells arranged closely and compactly without intercellular spaces . The cells contain vacuolated protoplasts with a single nucleus but chloroplasts are absent . A waxy layer called .cuticle. is deposited on the external surface of the epidermis . Cuticle prevents the evaporation of water from the plant body . Trichomes are absent Numerous stomata are found in the epidermis through which exchange of gases occurs .
Epidermis gives protection to the inner tissues , helps in the exchange of gases and also prevents the evaporation of water .
Hypodermis : A distinct cortex is absent in Monocot stems . However a thick walled hypodermis is found beneath the epidermis .The cells of hypodermis are sclerenchymatous and are arranged compactly in 3-4 rows, without any intercellular spaces. It gives machanical strength of the stem .
Ground tissue : A major part of the stem is formed by an extensive soft , parencymatous tissue called the ground tissue . The peripheral layer consists of smaller cells while the inner layers show bigger cells . The cells of peripheral layers are chlorenchymatous and are connected with a assimilation of food materials .the inner layers of cells are concerned with storage of food materials . In monocot stem endodermis is absent .
Vascular bundles : Numerous vascular bundles are found scattered irregularly in the ground tissue . This kind of arrangement is called .atactostele. .It is considered an on advanced character . The inner vascular bundles are bigger in size and far apart from one another . The outer vascular bundles are smaller and are close to one another and found in one or teo circles .
Each vascular bundle is oval in shape and shows xylem and phloem together on the same radius . There is no cambium between xylem and phloem at the upper side of the vascular bundle . Each vascular bundle is enchosed by a sheath of sclenrenchymatous fibres . Hence it is called fibro vascular bundle .
Xylem consists of tracids , vessels ,fibres and parenchyma . Xylem vessels are few in number (4) and are arranged in "Y" shape . one or two protoxylem cells are crushed forming lysigeneous cavity called protoxylem lacunae which store water pholem consists of sieve tubes and companion cells . Phloem parenchyma is absent Medulla , Medullary rays and pericycle are also absent .