Brief notes on the Internal structure of stem of maize (Zea mays)

A thin transverse section of the young maize stem reveals the following inte structure from the periphery to the centre.

(i) The outline of the stem is circular.

(ii) Epidermis: This is the outermost layer of cells which is usually single layered. It is covered with a thick cuticle and bears few stomata.

(iii) Hypodermis: This forms a narrow zone of sclerenchyma, usually two or three layers thick. It occurs below epidermis.

(iv) Ground tissue: The entire tissue lying inside the epidermis, except for the vascular bundles, is known as the ground tissue. The ground tissue is not differentiated into cortex, endodermis, pericycle and pith. It consists of rounded parenchymatous cells with distinct intercellular spaces.

(v) Vascular bundles: The vascular bundles are many in number and are of variable size. They are collateral and closed and lie scattered in the ground tissue.

The peripheral vascular bundles are smaller in size than the central ones. Eacvascular bundle is oval and is more ores completely surrounded by a sheath of sclerenchyma which is specially developed on the two sides – upper and lower.

The ascular bundles are conjoint, collateral, end arch and closed. The vascular bundle consists of two parts, xylem and phloem.

(a) Xylem: The xylem consists of four distinct vessels arranged in the form of a Y, and a small number of tracheids arranged irregularly. Two smaller vessels lying at the arm base constitute the protoxylem.

The two bigger vessels lying laterally constitute the Meta xylem, the lowermost protoxylem vessels open into a cavity called water congaing cavity. Besides, wood fibers occur associated with tracheids in between the two big pitted vessels. Thin walled wood (or xylem) parenchyma surrounding the water containing cavity occurs in the protoxylem.

(b) Phloem: The phloem lies outer to the xylem. It consists of sieve tube elements and companion cells. Phloem parenchyma is absent. The outermost portion of the phloem, which is a broken mass, is the protophloem, and the inner portion is the Meta phloem.