Answer:
Providing a controlled source of water vapour through which water can be vaporized into the plant envoirment.
Explanation:
Humidity ratio is the ratio of the mass of water in air to the mass of dry air. Humidity is needed in some conditions where the air is very dry. In a very dry air setting, there can be excess moisture loss from the plant surface, increasing the Humidity ratio can counter this effects and reduce excess moisture loss.
