Dicot Stem Cross Section

This is a cross-section (transverse section) of a typical herbaceous dicot stem. Its tissues are laid down in a characteristic manner.

EPIDERMIS
The outer layer, one cell thick, is the 'epidermis'. Some of these cells bear multi-cellular hairs or 'trichomes', which are beneficial for water conservation and defence. Because green stems can photosynthesise, the epidermis also contains 'stomata'. Just like leaves, the epidermis is covered with a waxy layer of cutin, the 'cuticle'.

CORTEX
The cortex comprises tissue located between the vascular blundles and the epidermis, often split into two layers. The outer layer is composed of collenchyma cells whose unevenly-thickened walls give flexible support to the growing plant. And, because it is a living material, can grow as the plant grows. The outermost collenchyma cells may contain chloroplasts, whose chlorophyll facilitates phososynthesis.

Below the collenchyma, the remainder of the cortex consists of unmodified parenchyma cells.

VASCULAR BUNDLES
In dicot stems, these are always arranged with the phloem towards the outside and the xylem towards to the centre. This has been described elsewhere (see 'Vascular Bundle Of Young Dicot Stem, Cross Section')

In dicots, the vascular bundles are arranged in a ring running the whole length of the stem, and connecting with the stele of the root and with the midribs of the leaf veins.

These bundles give much support, especially when a pericyle is present whose tightly-packed, lignified sclerenchyma fibres are extremely tough, forming a bundle, or cap, between the bundle and the cortex.

PITH
This is parenchyma packing material which forms the centre portion of the stem. In some plants, this is missing and the centre is hollow and often filled with water.

See also: 'Cross Section Of Young Dicot Root'