Dicotyledonous Stem

The transverse section of a typical young dicotyledonous stem shows a clear zonation from the outside to the centre.

• The epidermis is the outermost protective layer of the stem. It is covered with a thin layer of cuticle and may bear trichomes and a few stomata.
• The cells arranged in multiple layers between the epidermis and the pericycle constitute the cortex, which consists of three sub-zones:
  • the outer hypodermis, made up of a few layers of collenchymatous cells lying just below the epidermis, which provide mechanical strength to the young stem;
  • the cortical layers below the hypodermis, consisting of rounded, thin-walled parenchymatous cells with conspicuous intercellular spaces; and
  • the innermost layer of the cortex, the endodermis, whose cells are rich in starch grains, so that this layer is also referred to as the starch sheath.
• The pericycle is present on the inner side of the endodermis and above the phloem, in the form of semi-lunar patches of sclerenchyma.
• In between the vascular bundles there are a few layers of radially placed parenchymatous cells which constitute the medullary rays. …