Hydrotropism is the growth movement in response to unilateral stimulus of water. Roots are positively hydrotropic because they bend towards the source of water.

Experiment to demonstrate hydrotropism-

Germinate few seeds in moist dust in ground. After sometime you will observe that radicles start coming out of the ground but they start bending and again enter the moist saw dust. This happens because roots are positively hydrotropic. They bend towards the source of water i.e. moist sawdust in this case.