This is a function of velamen

The correct option is absorption of moisture from air.

What is Velamen?
Velamen is a specialized, multi-layered, and spongy tissue that forms the outer epidermal layer of the aerial roots in epiphytic plants, such as orchids and certain bromeliads.

Structure and Function:
1. Epiphytic Habitat: Epiphytic plants grow non-parasitically on other plants, often high up in the forest canopy. Because their roots are suspended in the air and do not reach the ground, they cannot absorb water from the soil.
2. Hygroscopic Nature: The cells of the velamen tissue are dead at maturity, hollow, and possess highly hygroscopic (moisture-attracting) cell walls.
3. Moisture Absorption: When the atmosphere becomes humid or during rain and dew formation, these spongy cells rapidly absorb water vapor and moisture directly from the surrounding air and store it temporarily.
4. Protection: Besides absorbing moisture, the velamen also protects the underlying living tissues of the root from mechanical damage and excessive water loss (transpiration).

Thus, the primary function of the velamen tissue is to facilitate the absorption of moisture from the air, enabling epiphytic plants to survive without soil-based water sources.