Question

Velamen found in epiphytic roots is meant for:
a. Absorption of water from host
b. Absorption of water from air
c. Perennation
d. Protection

Answer 1

An epiphyte is defined as a plant that grows on another plant. Epiphytic roots are hygroscopic roots that develop in some types of orchids, which later can grow as epiphytes on branches and trunk of trees.

Complete answer:
The main characteristic of these epiphytic roots is that they hang freely in the air. The stele in epiphytic roots has a very small diameter. Stele is covered by a cortex, and the cortex is surrounded by a specialized layer of exodermis. The exodermis is surrounded by a thick layer of many cells, known as Velamen. It is a modification of epidermis and is a spongy layer that covers epiphytic and semi epiphytic roots in some plants, such as in orchids.

Sometimes the roots of orchids show symbiotic association with bacteria or fungi that helps in fixing nutrients from the air.

Velamen, in the orchids, is a covering layer of whitish-gray colour when dry, and greenish when wet. The root tip always appears green in colour. Velamen emerges by the division of a special tissue from the tip of the root. If the cells of the velamen are dead, they diffuse light, and thus it appears grey or white. Once it absorbs water from the atmosphere, the cells become transparent and it appears green in colour.

It has the ability to absorb nutrients and moisture from the atmosphere, and sometimes sticks the plant to the substrate.

Hence, the correct answer is option (B).

Additional information:
Velamen also protects the roots from mechanical damage by shielding the vascular tissues present in the root cortex, and protecting the roots from water loss due to transpiration. Velamen also protects the cells underlying it from harmful Ultraviolet rays.

Note: Although velamen helps in protecting the epiphytic roots against damage, its main role is in absorption of water from the atmosphere, that’s why the correct option is absorption of water from air, and not protection.