n. 1. (Bot.) A tendency towards moisture. [ 1913 Webster ]

2. (Bot.) In a broader sense, any curvature or turning induced in certain growing plant organs under the influence of moisture.

☞ When the movement is toward the moisture, as is the case in most roots, the phenomenon is called positive hydrotropism; when away from the moisture, as in the case of hyphae of certain fungi, negative hydrotropism. [ Webster 1913 Suppl. ]