from
The Collaborative International Dictionary of English v.0.48
Hydrotropism \Hy*drot"ro*pism\, 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.
Note: 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.]