Ground tissue

From Freepedia

The types of ground tissue found in plants develops from ground tissue meristem and consists of three simple tissues:

Parenchyma (have retained their protoplasts)
Collenchyma (have retained their protoplasts)
Sclerenchyma (have lost their protoplasts in mature stage, i.e. are 'dead')

Parenchyma is the most common ground tissue, it forms e.g. the cortex and pith of stems, the cortex of roots, the mesophyll (photosynthetic cells), the pulp of fruits and the endosperm of seeds. Parenchyma cells are capable of cell division, even after maturation (i.e. they are still meristematic). Parenchyma cells have a variety of functions;

photosynthesis (may then be called Chlorenchyma /Mesophyll cells),
gas exchange (Aerenchyma),
storage,
secretion (e.g. Epithelial cells lining the inside of resin ducts)
other specialised functions.

Collenchyma tissue have many similarities with Parenchyma tissue, but the cells are generally longer, and are more polygonal (in cross-section). Collenchyma cells are mostly found in supporting structures of plants, like in the cortex and in leaves (and are especially important for mechanical support in non-lignified or herbaceous plants). The cell walls of collenchyma cells have generally thicker layers of cellulose, and especially in the corners.

Sclerenchyma tissue consist of cells with very hard and (in most cases) lignified cell walls. The two main types are fibres (long and tapered cells in e.g. wood and bark) and sclereids (e.g. bark, seed coats, nutshells). Their function is mainly mechanical support and protection.