Roots

Root morphology (see Figure 5.3). The function of the root system is to take up water and mineral nutrients from the growing medium and to anchor the plant in that medium. Its major function involves making contact with the water in the growing medium. To achieve this it must have as large a surface area as possible. The root surface near to the tip where growth occurs (cell division in the meristem, see p93) is protected by the root cap. The root zone behind the root tip has tiny projections called root hairs reaching numbers of 200-400 per square millimetre, which greatly increase the surface area in this region (see Figure 5.4). Plants grown in hydroculture, e.g. NFT (p394), produce considerably fewer root hairs. The loss of root hairs during transplanting can check plant growth considerably, and the hairs can be points of entry of diseases such as club root (see Chapter 15). Figure 5.4 shows that the layer with the root hairs, the epidermis, is comparable with the epidermis of the stem (see stem structure); it is a single layer of cells which has a protective as well as an absorptive function.

A taproot is a single large root which will have many lateral roots growing out from it at intervals.

A fibrous root system consists of many roots growing out from the base of the stem.

Two types of root system are produced; a taproot is a single large root which usually maintains a direction of growth in response to gravity (see geotropism) with many small lateral roots growing from it, e.g. in chrysanthemums, brassicas, dock. In contrast, a fibrous root system consists of many roots growing out from the base of the stem, as in grasses and groundsel (see Figure 5.3).

Primary roots originate from the lower end of the hypocotyl.

Secondary roots are branches of the primary roots.

Adventitious roots grow in unusual places such as on the stem or other organ.

Root hair zone

Long view of root tip region

Figure 5.4 Root tip showing the tip protected by root cap, and root hair zone

Root hair zone

Root tip Root cap

Long view of root tip region

Figure 5.4 Root tip showing the tip protected by root cap, and root hair zone

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