ROOT MORPHOLOGY & TYPES

DEFINITION OF ROOT:

Roots are positively geotropic structures of the plant that derive nourishment from the soil and hold the plant in its place.

Characteristics of Root:

1. Roots show positive geotropism, i.e., they grow towards the ground / underground.

2. Roots show negative phototropism, i.e., they grow away from the direction of light. ( Photo = light, tropic = respond towards stimulus).

3) Roots bear UNICELLULAR ROOT HAIRS, which are the MAIN ABSORPTIVE ORGANS of the root.

4) Roots are non green structures.

5) Roots lack nodes and internodes.

ROOT MORPHOLOGY: A root comprises of the following regions:

1. Root Cap : – Protective structure that secretes oil for penetration of root into the soil.

– Multiple root caps are present in Pandanus.

– Root Cap is enclosed in a Root Pocket in hydrophytes ( acquatic plants) .

2. Region of Cell Division / Apical Region : – – It is the main active growing region of the root.

– It is made up of parenchymatous cells.

3. Region of Elongation : – Here, the new cells formed in the apical region of the root increase in size (cellular expansion) , leading to an increment in the length of the root.

4. Region of Maturation : – Here, the elongated cells differentiate into cells of specific function.

– For example, some of the epidermal cells differentiate to form Root hairs, which perform the function of increasing surface area for absorption of water and minerals.

– Root hair arise from the region of maturation ONLY.

TYPES OF ROOT SYSTEMS :

1) Tap Root System

– Tap roots develop directly from the radicle.

– They bear primary, secondary and tertiary roots.

– Primary root persists for long life.

– Tap roots are ALWAYS UNDERGROUND.

– They show Deep Soil Penetration.

2) Adventious Root System

– Adventious roots develop from any part of the plant besides the radicle.

– Does not bear primary, secondary and tertiary roots.

– Primary roots does not persist for long life.

– Usually AERIAL.

– No deep soil penetration.

– Types of Adventious roots

1. FIBROUS ADVENTIOUS ROOTS– Primary roots get replaced by fibres arising in clusters from the base of the stem.

e.g. Allium cepa (Onion), Oryza sativa (Rice), Triticium vulgare ( Wheat) .

2. FOLIAR ADVENTIOUS ROOTS (Foliar/Foliage = in relation to leaf): Roots that arise from leaves.

e.g. Pogostemon patchouli – Foliar adventious roots arise from the petiole. In Bryophyllum – Foliar adventious roots arise from the margin of leaf blade.

3. TRUE ADVENTIOUS ROOTS : Arise from Nodes & Internodes.

e.g. Prop roots, Climbing roots