| 释义 |
paratonic, a.|pærəˈtɒnɪk|
[f. Gr. παρα- para-1 1 + tonic; cf. Gr. παράτον-ος stretched beside or beyond.]
1. Path. Relating to overstrain.
1857Mayne Expos. Lex., Paratonia,..an overstraining. Paratonicus, of or belonging to Paratonia: paratonic.
2. Bot.
a. [First formed in this sense as G. paratonisch (J. Sachs Lehrb. der Bot. (1868) iii. i. 517).] Applied by Sachs to the effect of the varying intensity of light in causing the movements of ‘waking’ and ‘sleeping’, i.e. opening and closing of the leaves, etc. in certain plants; in general, applied to plant movements caused by external stimuli (e.g. tropisms and kineses).
b. Applied to movements of leaves, or of growing organs, caused by external stimuli, as light or mechanical irritation.
c. Applied to the effect of light in retarding growth in most growing organs, as district from its stimulating effect on leaves.
1875Bennett & Dyer tr. Sachs' Bot. 677 In most leaves endowed with periodic movements the paratonic influence of light is so strong that it neutralises them. Ibid. 678 Both the periodic and paratonic movement..is lost when they [the plants] have remained in the dark for a considerable time, such as a whole day; in other words, they become rigid by long exposure to darkness. 1878McNab Bot. 136 In other cases the nutations are due to the action of external causes on growth. Such nutations are called paratonic or kinetic. 1910J. M. Coulter et al. Textbk. Bot. I. ii. 454 The terminal leaflet of Desmodium gyrans, like leaves of other members of the bean family, exhibits paratonic movements (i.e. those due to special stimuli, not tonic; opposed to autonomic). 1973A. Cronquist Basic Bot. xxvi. 412/2 Some growth movements are self-controlled (autonomic); others are induced by external stimuli (paratonic)... Paratonic movements are further classified as tropisms and nasties.
Hence paraˈtonically adv., in a paratonic manner (in quot. in sense 2 a).
1880C. & F. Darwin Movem. Pl. 123 But cotyledons, besides being heliotropic, are affected paratonically (to use Sachs' expression) by light. |