Hydrotropism
GROWTH OR MOVEMENT IN A SESSILE ORGANISM TOWARD OR AWAY FROM WATER, AS OF THE ROOTS OF A PLANT
Hydroptropism
Hydrotropism (hydro- "water"; tropism "involuntary orientation by an organism, that involves turning or curving as a positive or negative response to a stimulus")condensed definitions, Webster's New Collegiate Dictionary is a plant's growth response in which the direction of growth is determined by a stimulus or gradient in water concentration. A common example is a plant root growing in humid air bending toward a higher relative humidity level.