Why Leaves of some plants wilt during Afternoon?

In some plants e. g. balsam, the leaves of the plants wilt during the midday in spite of the fact that there is pleanty of water in the soil. In such cases  the rate of transpiration during midday exceeds the rate of absorpation of water by the roots . The cells therefore lose turgidity . in the eveing or during the night the stomata are constricted and the temperature is not very high, therefore there is no loss of water through transpiration and turgidity of thr leaves is re-acquired and the sand out erect.

PERMANENT WILTING

Wilting

Wilting refers to the loss of rigidity of non-woody parts of plants. This occurs when the turgor pressure in non-lignified plant cells falls towards zero, as a result of diminished water in the cells. The process of wilting modifies the leaf angle distribution of the plant (or canopy) towards more erectophile conditions.

Lower water availability may result from:

    drought conditions, where the soil moisture drops below conditions most favorable for plant functioning;
    the temperature falls to the point where the plants vascular system can not function.
    high salinity, which causes water to diffuse from the plant cells and induce shrinkage;
    saturated soil conditions, where roots are unable to obtain sufficient oxygen for cellular respiration, and so are unable to transport water into the plant; or
    bacteria or fungi that clog the plant's vascular system.

Wilting diminishes the plant's ability to transpire and grow. Permanent wilting leads to plant death. Symptoms of wilting and blights resemble one another.

In woody plants, reduced water availability leads to cavitation of the xylem.

Wilting occurs in plants such as Balsam and tulasi.