Roots anchor the plant firmly in the soil and prevent its being blown away by wind. They absorb water and mineral salts from the soil and pass them to the stem. They also act frequently as organs for food storage. In floating or submerged aquatic plants the root system may be poorly developed or totally absent.
Types of Root System
The two main types of root systems in plants are
- the tap-root system and
- the fibrous-root system
Fig: Types of Root System
- Tap-root System
When a seed germinates, a single root grows vertically down into the soil. The embryonic part called radicle gives rise to the root system and the plumule gives rise to the shoot system. Later, lateral roots grow from the main root at an acute angle, outwards. From these laterals, other branches may arise. The root system, in which a main root is recognizable, is called a tap root system.
- Fibrous-root System
When a seed of a grass or cereal group germinates, several roots grow out at the same time and laterals grow from them. There is no distinguishable main root. Such a system is called a fibrous root system.
Root Cap - It is the thimble-shaped mass of parenchyma cells covering each root tip. Protects tissue from damage.
Functions in Gravity Perception
Region of Cell Division - Composed of apical meristem in the center of the root tip. Most cell division occurs at the edge of the inverted cup-shaped zone.
Region of Elongation - Cells become several times their original length. Vacuoles merge.
Region of Maturation - Most cells differentiate into various distinctive cell types. Root hairs form. Absorb water and minerals and adhere tightly to soil particles. Thin cuticle.
Apart from their basic functions of anchoring the plant and absorbing nutrients and water from the soil, roots also serve as storage organs for food in many plants. These roots appear swollen with storage of food in many plants and assume various shapes in various plant species. A swollen root tapering at both ends is termed fusiform (e.g. radish). Globular roots tapering abruptly, as in turnip and beetroot, are termed napiform. Conical roots are found in carrots and roots without a definite shape as found in Mirabilis are called tuberous roots.
When roots grow directly from the stem, as they do in bulbs, corms, rhizomes and runners, they are called adventitious roots. Typical examples of plants bearing adventitious roots are grasses, the banyan tree and mangroves. There are many modifications of the adventitious roots. In certain plants such as sweet potato and Cassava the adventitious root are swollen near their tops with food reserves forming what are called root tubers. Storage roots occur in clusters in Asparagus and Dahlia and these are called fasciculated roots.
Fig: Root Tuber of CassavaIn Portulaca the adventitious roots have swollen regions at frequent intervals, and hence are called beaded. Adventitious roots give additional support to many plants. These supportive structures may be in the form of massive, pillar-like structures as those in the banyan tree (prop roots) or they may be clusters of roots growing downward from the base of the plant (stilt roots). In certain plants adventitious roots develop chlorophyll (e.g. Tinospora and Trapa) and take part in photosynthetic activity. These are called assimilatory roots. In certain parasitic plants the roots penetrate the host tissue to derive nutritive materials. These root structures are called haustoria.