Question

On cool nights, following sultry days, water is found at the tips and margins of tomato leaves in the form of dew drops. Every drop marks the location of ______.
A. Stomata
B. Lenticels
C. Hydathode
D. Trichome

Answer 1

Hint:Guttation should not be confused with dew, condensing the plant surface from the atmosphere. Guttation normally occurs in the night.

Complete answer:
The movement of water through a plant and its evaporation from an aerial region, including leaves, stems and flowers is transpiration. Water is needed for plants, but for metabolism and growth only a small amount of water taken by the roots is used. The other 97-99.5 percent is lost by transpiration and guttation. Guttation is the exudation of xylem sap drops on the tips or borders of some vascular plants' leaves including herbs and a variety of fungi. Guttation should not be confused with dew, condensing the plant surface from the atmosphere. Guttation normally occurs in the night.

Transpiration is typically not occurring at night because most plants have their stomata closed. Water reaches plant roots when there is high soil moisture level, as the roots' water capacity is smaller than in the soil solution. The water accumulates and creates a small root pressure in the plant. Water is guided by the root pressure through the special tips or edge of leaves, hydathodes or glands, which form drops. Root pressure gives this flow a boost rather than a transpirational pull. Guttation is most evident when transpiration is suppressed and relative humidity, such as in the nighttime, is high. On cool nights, following sultry days, water is found at the tips and margins of tomato leaves in the form of dew drops. Every drop marks the location of hydathodes.

Thus, the correct answer is option C. i.e., Hydathode.

Note:As a result of guttation, water droplets were observed. Guttation is the loss of water, usually from edges and leaf margins, in liquid condition from uninjured areas of plants. In this water emerges from the hydathodes. A hydathode is a leaf epidermis opening or a pore around which many thin walled parenchyma cells are clustered. It happens in the night or early morning, when humidity is high and transpiration is less.