nastic, -nastic; nasty, -nasty; -nastism +
(Greek: nastos, pressed close, crammed full; firm, solid)
2. The curvature of part of a plant stimulated by a widely spread or a scattered stimulus.
2. A downward bending of leaves or other plant parts, resulting from excessive growth of the upper side.
In plant physiology, the state in which more vigorous growth occurs in the upper surface of an organ, such as in an unfolding leaf, causing a downward curvature.
The leaf movements of the Venus flytrap Dionaea muscipula following a tactile stimulus, and the rapid collapse of the leaflets of the sensitive plant Mimosa pudica are examples of haptonasty.
2. An upward bending of leaves or other plant parts, resulting from growth of the lower side.
In plant physiology, the state in which more vigorous growth occurs in the lower surface of an organ, such as a young fern frond, causing an upward curvature.
2. Relating to a response of a plant part; such as, growth or a loss of turgidity; to external stimuli that is independent of the direction of origin of such stimuli.
3. The movement or growth of cellular tissue on one surface more than on another one, as in the opening of petal or young leaves.
Movements are rapid, reversible responses to stimuli; such as, water, temperature, humidity, light, etc. Nastic movements occur as a result of changes in water pressure within specialized cells or differing rates of growth in parts of the plant.
The opening and closing movements of many flowers, and the responses of leaves to changes of temperature and light, are externally directed, or paratonic, nastic movements. Specialized plants, such as the insectivorous sundew, move in response to the touch and chemical stimuli of captured insects.
Nastic movements are responses to stimuli that uniformly affect the plant or else elicit a uniform response regardless of the direction they come from, whereas tropisms are movements in response to stimuli coming from one direction; geotropism, for example, is the response to gravity. The distinction between nasticisms and tropisms is sometimes unclear.