Question

Which root amongst the following grows against gravitational force?

• A. Prop roots
• B. Stilt roots
• C. Buttress roots
• D. Pneumatophores

Answer 1

The correct option is D Pneumatophores

Roots are plant structures that arise from the radicle and grow towards the soil. The feature of plant roots growing towards the soil or directional growth of an organism towards gravity is known as geotropism. Hence, roots are positively geotropic.
But plants that grow in salt lakes, mangroves or swamps face deficiency in oxygen. Hence, they possess horizontal cable roots which give rise to vertically upward aerial roots at short intervals. These negatively geotropic roots are called pneumatophores or respiratory roots. E.g. Rhizophora.


When root arises from branches of plants and grows downward toward soil (positive geotropism) to support the plant structure, the root modification is known as prop roots or pillar roots. E.g. Banyan tree.


When roots arise obliquely from the lower nodes of the stem towards the soil (positive geotropism), the type of root is known as stilt root. E.g. Maize.


Buttress roots are plate-like aerial extensions of the lateral shallow roots that grow in nutrient poor tropical forest soils. As these roots are shallow, the buttress roots provide support and prevents the tree from falling over.