-nasty Also -nastic.
[Greek nastos, squeezed together, plus -y3.]
In botany, a nastic movement is one made by a plant in response to an external stimulus which does not dictate the direction of the movement (one that does is a tropism); an example is the opening of flowers in response to increasing temperature. A few nouns indicate types of nastic behaviour: epinasty (Greek epi, upon, near to), the bending downward of a part of a plant caused by increased growth on its upper surface; nyctinasty (Greek nux, nukt-, night), periodic movement of flowers or leaves caused by nightly alterations in light intensity or temperature; seismonasty (Greek seismos, earthquake), a movement made in response to a mechanical shock. Related adjectives are formed using -nastic: hyponastic, nyctinastic,