Roots are helpful for the plants as they provide support to the stems as well as absorb water and minerals from the soil. Roots also store food materials. Root system is present in two types. They are primary root and secondary root.
Primary root originates from the embryo and is also called as tap root system. The branches in the tap root system are fibrous and are known as secondary roots. The primary root system of plant lives for short period and it is followed by secondary root system. The secondary roots are permanent roots in monocots like grasses. The roots from rhizomes, bulbs, corms and tubers are adventitious roots. They also arise from the aerial stems as well as from the stem cuttings and root cuttings. The plants like Ficus, Rhizophora and Pandanus sps., extend down the adventitious roots such that these roots act as support to the horizontal branches.
Root hairs are specialized extensions of the cells that can penetrate into the soil particles. The outer wall of the cell is expanded and forms an outgrowth tubular in shape. This outgrowth will make contact with the soil and absorb minerals and water from the soil. The mineral nutrients and water move from the soil into the root hairs followed by their entry into the rootlets and then into main root which transports water and minerals into the stem and leaves. More number of root hairs are formed at the tip of the roots and they are short-lived in most of the plants. The transplantation of plants from one place to another has to be done carefully to avoid the loss of these root hairs which help in the proper absorption of water and minerals.
They are primary roots which give rise to several lateral roots or secondary roots. Tap roots divide, become fleshy and travel deep into the soil. Tap roots are seen to be present in perennial herbs like Quercus sps., Citrus sps., Daucus carota, and Taraxacum officinale, so on.
These roots do not have a separate primary root. They have numerous small thread like roots that are similar in size and originate from the stem base. Fibrous roots spread on the soil surface instead of entering deep and straight into the soil. Fibrous roots are seen in grasses and in some shrubs.
The fleshy roots are the storage places for food. They store excess food during the winter and adverse conditions such that the plant can make use of the food for its regrowth process. Some of the plants that come under this category are carrot (Daucus carota), turnips (Brassica rapa), beet root (beta vulgaris). These plants have tap root or main root storing the food. The secondary roots are transformed into tubers in the case of plants like sweet potatoes (Ipomea batatas) and Dahlia sps.
The aerial roots are formed in many of the land plants as well as in water plants. They are formed in the moist atmosphere. The aerial roots allow the climbers like Philodendron sps., to take the support of the host. The aerial roots in the epiphytes like orchids not only take the support of the host plants but, will absorb water from the air. The aerial roots are fleshy in many cases as they store water transforming into reservoirs.
The pneumatophores are developed in the plants like Taxodium distichum, also called as Bald Cypress. The ground or water, cuts off the air from the roots and make the trees to develop knees. These knees are protruding on the surface, allowing the plant to take in air.