We all know how important roots are for the survival of a plant. Though we may not be able to see them sometimes, however, they are always doing their job.
Roots are not only one of the important structures present in the plants but they also perform various critical functions. They play a major role in the life processes. Interestingly, not all plants have roots, some plants like mosses and liverworts lack the root system.
Types of Root System
All roots have almost similar functions but they vary in structure and the site of origin. So, based on these criteria, roots are mainly divided into three types, that is,
- Taproot System
- Adventitious Root System
- Fibrous Root System
Let us study these root systems in detail.
Taproots appear from the radicle of the embryo of a germinating seed. In the taproot system, there is one main root from which lateral root branches originate.
Upon germination, the first root that arises from the radicle is the main cylindrical root, also known as the primary root, which grows vertically downward. From the main root, first-order roots arise which are known as the secondary roots. And, then, from these secondary roots, the second-order roots arise which are known as the tertiary roots. On the tip of tertiary roots, there are present thin hair-like structures known as the ‘Rootlets.’ The primary root is the most prominent, thickest, and longest of all. Taproots gradually become narrow towards the tip.
Taproots are present in dicotyledonous plants. Taproots can persist for a lifetime but are often replaced by the fibrous root system in the later stages of plant development because the radicle of most of the plant species dies after germination.
Taproots tend to be deep-rooted and are difficult to uproot. If during the process of uprooting a tap root plant, the root breaks off, the part that is left in the soil often sprouts again.
Taproots grow in acropetal succession, that is, the youngest is present at the growing end while oldest towards the base. Rootlets are very delicate structures and are the ultimate branches of a tap root system. They are responsible for water absorption in plants. Primary roots always grow in the vertical orientation while secondary and tertiary roots grow in the horizontal orientation.
Examples of the taproot system can be seen in a variety of plants, even the ones present in the kitchen gardens, like;
- Sugar beet
- Rose plant
Adventitious Root System
The adventitious root system is the opposite of the taproot system. Adventitious roots grow from other parts of the plant except for the radicle or its branches. And instead of having one primary root from which the branches arises, in adventitious roots, there are numerous morphologically similar roots arising from the same node.
Adventitious roots are generally seen growing from aerial parts of the plants. They can arise from injured roots, stem, internodes, branches, or any other tissue. They are formed from the pre-induced root primordial cells.
Adventitious roots commonly occur in monocots but also in some dicots, such as Ivy, Strawberry, Clover, and Willow. Most of the aerial roots are adventitious. Adventitious aerial roots of many tropical trees are quite usual. For example,
- Ficus produces free-hanging adventitious roots.
- Liana’s roots also arise from the aerial organs.
Adventitious roots can grow from the leaf and stem cuttings when placed in the soil. You can simply re-grow the plants with adventitious roots with their leaves or stem cuttings. Hormones also induce the development of adventitious roots.
Examples of adventitious roots include;
- Hanging roots of a Banyan tree provide it mechanical strength.
- Prop roots of Mangrove trees provide them with steady support. They arise from the branches and grow downwards into the soil.
- Climbing roots of Betel help them with getting a firm hold on the structure that they are climbing.
- Buttress roots of Fig trees arise from the base of a stem and support the plant.
Fibrous Root System
Fibrous roots arise from the base of the stem or the nodes of a horizontal stem; for example; grass plants.
Fibrous roots do not penetrate deep into the soil. They begin as a single main root like a tap root system, but, later on, spread like a mat on the ground with only a few roots deep into the soil.
Unlike adventitious aerial roots, fibrous roots are present underground. Leaves with parallel venation have a fibrous root system.
Examples of plants with fibrous roots;
- Palm tree (Arecaceae)
- Rice (Oryza sativa)
- Grasses (Poaceae)
- Maize (Zea mays)
- Wheat (Triticum)
- Millet (Pennisetum glaucum)
- Onion (Allium cepa)
- Sweet potato (Ipomoea batatas)
- Asparagus (Asparagus officinalis)
Let us now learn about some of the major functions of a root system;
Functions of the Root System
- Roots absorb water and minerals from the soil and transport them to the upper parts like stem and leaves of the plant. The water and minerals are carried from roots to the upper parts of the plants in an upward movement, against the gravity. Therefore, it requires some force. This force is provided by the transpirational pull due to the process of transpiration going on in the leaves.
- Roots also provide anchorage to the plants and keep them attached to the soil by binding the soil around the roots. This is the reason why it is difficult to uproot a plant by hands.
- Roots are used to store food; for example, fleshy roots like Carrot, Radish, Beet, Turnip, and Mirabilis.
- Roots play an essential role in binding the soil. Roots help in preventing soil erosion and land sliding in the hilly areas.
- Roots of plants like Corms, Stem Tubers, Rhizomes, and Stolon participate in vegetative reproduction.
- In some week stemmed plants, roots help in clinging and, hence, climbing roots; for example, Money Plant, Betel, Ivy, etc.
- Roots also take part in nitrogen fixation with the help of nitrogen-fixing bacteria present in the soil. For example, nodulated roots Of Pea, Bean, Gram, Fenugreek, etc.
- Roots of some plants are present above the ground and known as Aerial Roots. For example, pneumatophores are the type of specialized aerial roots present in Mangrove plants. They help the plant to breathe.
- Roots of mangrove and epiphytic orchids play a significant role in the photosynthesis. They become green upon exposure to light and start producing energy. There is even a leafless orchid (Dendrophylax lindenii) which solely depends upon its roots for energy production.