Chemotropism is the movement due to chemicals. Chemotropism is best exhibited by pollen tube (i.e., growth of pollen tube in the stigma). Hydrotropism is a paratonic directional growth movement of curvature caused by unilateral stimulus of water. Roots are positively hydratropic. The non directional movement of curvature in response to temperature changes is termed as thermonasty
e.g., Crocus, Tulipa. Thermotaxis is movement in response to stimulation of heat.