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Root Growth
(Canadian Campbell, Fig. 35.13)
The first organ of the embryo to emerge and become established is the root. The root apical meristem consists of a large number of dividing cells located at the root tip. This meristem produces all the cells that will constitute the main axis of the root as well as the cells of the protective root cap.
Examine the prepared slide of a root tip of:
Note: the root cap and dividing cells of the root meristem. Within the meristematic region the cells are small, dense staining and contain prominent nuclei. Many of these cells are in various stages of mitosis and numerous mitotic figures should be visible. Examine the more basal regions of the root axis. The cells in these areas were derived from the root apical meristem. These cells are wider, more elongate and more vacuolate than the meristematic cells.
Root Structure
(Canadian Campbell ed. Fig. 35.14)
The main functions of the root are anchorage, absorption of water and solutes, storage and conduction. The absorption function is greatly enhanced by numerous root hairs which effectively increase the total surface area of root epidermal cells and are differentiated in regions of the root that have ceased elongation.
Examine the primary root of the radish seedlings and note the numerous root hairs
Concurrent with root hair development the internal tissues of the root differentiate into mature primary tissues. The central region of the root differentiates into the stele (vascular cylinder) composed of three main tissues: xylem, phloem and pericycle. The pericycle is composed of parenchyma cells that may during the course of development become meristematic and initiate the apical meristem of lateral (secondary) roots. The pericycle also initiates or contributes to the lateral meristems (cork cambium and vascular cambium) in those roots which exhibit a secondary growth phase. Between the pericycle and cortex there is a uniseriate cylinder of cells called the endodermis. Between the endodermis and the epidermis of the root is the cortex. The cortex is mainly composed of parenchyma cells containing an abundance of starch granules.
Note the above mentioned features of root structure. You should also be able to give the major functions of the cells and tissues present in the mature root.
