Epiphytes like Vanda develop special layer of absorptive tissue velamen consisting of 4 or 5 layer os long polygonal cells. Velamen is formed by

The correct option is Hanging roots.

Epiphytes are plants that grow on the surface of other plants, typically trees, for physical support rather than obtaining nutrients from them. Because their roots are not anchored in the soil, they have adapted specialized structures to absorb moisture and nutrients directly from the atmosphere, rain, and surrounding debris.

Vanda, a well-known genus of epiphytic orchids, develops two main types of aerial roots: clinging roots and hanging roots (also known as aerial absorptive roots).
The clinging roots serve primarily to anchor the plant securely to the bark of the host tree. On the other hand, the hanging roots dangle freely in the air. These hanging roots are surrounded by a specialized multi-layered, sponge-like tissue called the velamen. The velamen is composed of four or five layers of dead, polygonal cells with thickened walls that efficiently absorb water from atmospheric humidity, mist, and rain. Therefore, the velamen is specifically formed by and covers the hanging roots of the epiphyte.