American Heritage® Dictionary of the English Language, Fourth Edition
- n. Growth or orientation of a sessile organism, especially a plant, toward or away from the light of the sun.
Century Dictionary and Cyclopedia
- n. In botany, the tendency of growing organs to bend toward or in some cases away from the light, due in the former case to the retarding influence exerted by the light upon their growth on the side of the highest illumination. Thus the stems of plants that are grown in a window, or under other conditions in which light falls laterally upon them, curve toward the light; and if their position is reversed, they soon turn again toward the side of greatest illumination. The leaves arrange themselves so that the rays of light fall as nearly as possible perpendicularly upon their upper surfaces, and the stem curves so as to direct its apex toward the sonrce of light. Organs which behave in this way are said to be affected by positive heliotropism or to be simply heliotropic. On the other hand, certain organs upon which light also falls laterally curve in an opposite direction—that is, the apex is turned away from the source of light. Organs exhibiting this kind of curvature are said to be negatively heliotropic or apheliotropic. This condition is most frequently observed in roots. A still further condition, which has been called
transverse heliotropismby Frank and dia-heliotropism by Darwin, is the condition under which certain organs tend to place their long axes perpendicular to the direction of the incident rays. The precise action of light in producing these various modifications is not well understood, but, as the studies of Vines have shown, it is probably largely due to modifications of the turgescence of the growing cells. Also heliotropy.
- n. The property of some plants of turning under the influence of light; either positively (towards the light) or negatively (away from the light)
GNU Webster's 1913
- n. (Bot.) The phenomenon of turning toward the light, seen in many leaves and flowers.
- n. an orienting response to the sun
- helio- + tropism (Wiktionary)
“Besides the algae in their skin, they had altered hormone levels with predispositions toward heliotropism and nudity, plus numerous other "improvements.”
“His very geographical situation was sufficient to turn the mind towards him, but the particular reason for that heliotropism on the part of his feminine neighbors was that he was an easy man for a woman to ask.”
“Since plants possess no nerves, this identity of animal with plant heliotropism can offer but one inference -- these heliotropic effects must depend upon conditions which are common to both animals and plants.”
“I tiptoed religiously by it, went on up to the big house where the three women slept, as if drawn to their abode by a sort of heliotropism.”
“They give the quintessence of laboratory experiments as to what are the effects of different energies such as light (heliotropism), electricity (galvanotropism), gravity (geotropism), etc., in their reaction and influence upon the movements and actions of living organisms.”
“Are we to suppose that the upper half of the body or eye had a positive heliotropism and the lower half a negative heliotropism?”
“The sensitiveness belonging to living substance, known by the names heliotropism, chemotropism, etc., is like a sketch of sensation and of the reactions following it; organic memory is the basis and the obliterated form of conscious memory.”
“Vienna (who has lately published a great book on heliotropism) finds that an intermittent light, say of 20 minutes, produces the same effect as a continuous light of, say 60 m.”
“Wiesner's papers on heliotropism are in the "Denkschriften" of the Vienna Academy, Volumes”
“And, yes, many sunflowers do follow the sun in the bud stage, with the young blooms turning east to west daily in a process called heliotropism.”
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