Hydrotropism, curvature expressing unequal growth (heterauxesis) induced by the proximity of moisture. Positive hydrotropism is curvature towards the moisture; negative hydrotropism, curvature away from it. If, for example, the roots from germinating seeds grow [under the influence of geotropism (q.v.) ] through holes in the bottom of a box soaked with moisture, they will bend backward, especially if the air be dry, towards the moist wood. This is positive. The rarer negative curvature is exhibited by the sporangiferons hyphee of the fungus Phycoinyces. The term hydrotropism was originally suggested by Darwin.