Internal structure of dicot stem

A plant whose seed contains two cotyledon or embryonic leaf is known as dicot. This article briefly focus about characteristics and anatomy of dicot stem. The microscopic structure of T.S. of sunflower (Helianthus annus) stem shows following distinct regions:

Epidermis; Cortex (hypodermis, general cortex, endodermis); Pericycle; Medullary rays; Vascular bundles and Pith.

(i) Epidermis is the outermost single layered covering of stem having no intercellular spaces. A thick cuticle layer is present on the outer surface of epidermis. Multicellular hairs are also present.

(ii) Several multi cellular hairs and stomata are present in the epidermis.

(iii) Cortex is distinguished into three layers, such as- Hypodermis, general cortex and endodermis.

(iv) Endodermis is the outermost layer of cortex having barrel-shaped parenchyma cells containing starch grains.

(v) Stele includes pericycle, vascular bundles, pith (medulla) and pith rays (medullary rays).

(vi) Vascular bundles:

  • Conjoint collateral or by-collateral and open
  • They are arranged in a ring
  • Meta-xylem lies towards the periphery while proto-xylem lies towards the centre.

(vii) Medullary rays are present in the stele. Example- Sun flower (Helianthus annus).