{ } n. [ Gr. &unr_; other + direction, way, &unr_; to turn: cf. F. allotropie. ] (Chem.) The property of existing in two or more conditions which are distinct in their physical or chemical relations. [ 1913 Webster ]

☞ Thus, carbon occurs crystallized in octahedrons and other related forms, in a state of extreme hardness, in the diamond; it occurs in hexagonal forms, and of little hardness, in black lead; and again occurs in a third form, with entire softness, in lampblack and charcoal. In some cases, one of these is peculiarly an active state, and the other a passive one. Thus, ozone is an active state of oxygen, and is distinct from ordinary oxygen, which is the element in its passive state. [ 1913 Webster ]

n. The habit of bending from the sunlight; -- said of certain plants. [ 1913 Webster ]

n. The apogeotropic tendency of some leaves, and other parts. [ 1913 Webster ]

n. (Med.) A condition of the system produced by long use of belladonna. [ 1913 Webster ]

n. [ Auto- + Gr. &unr_; to turn. ] (Plant Physiol.) The tendency of plant organs to grow in a straight line when uninfluenced by external stimuli. [ Webster 1913 Suppl. ]

n. (Bot.) The tendency of organs (as roots) of plants to assume a position oblique or transverse to a direction towards the center of the earth. [ 1913 Webster ]

n. (Bot.) A tendency of leaves or other organs of plants to have their dorsal surface faced towards the rays of light. [ 1913 Webster ]

n. [ Galvanic + Gr. &unr_; to turn. ] (Bot.) The tendency of a root to place its axis in the line of a galvanic current. [ 1913 Webster ]

n. [ Gr. ge`a, gh^, the earth + &unr_; to turn. ] (Biol.) A disposition to turn or incline towards the earth; the influence of gravity in determining the direction of growth of an organ. [ 1913 Webster ]

☞ In plants, organs which grow towards the center of the earth are said to be positively geotropic, and those growing in the opposite direction negatively geotropic. In animals, geotropism is supposed by some to have an influence either direct or indirect on the plane of division of the ovum. [ 1913 Webster ]

n. [ Helio- + Gr. &unr_; to turn. ] (Bot.) The phenomenon of turning toward the light, seen in many leaves and flowers. [ 1913 Webster ]

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.

☞ 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. ]

n. Isotropy. [ 1913 Webster ]

n. An affinity for neural tissues. [ WordNet 1.5 ]

n. [ From Gr. ny`x, nykto`s, night + &unr_; to turn. ] (Plant Physiol.) The tendency of certain plant organs, as leaves, to assume special “sleeping” positions or make curvatures under the influence of darkness. It is well illustrated in the leaflets of clover and other leguminous plants.

n. [ Photo- + Gr. &unr_; to turn. ] 1. (Plant Physiol.) The tendency of growing plant organs to move or curve under the influence of light. In ordinary use the term is practically synonymous with heliotropism. [ Webster 1913 Suppl. ]

2. (Microbiology) exhibiting movement in a direction toward (positive phototropism) or away from (negative phototropism) a source of light. [ PJC ]

n. [ Gr. sw^ma, sw`matos, the body + tre`pein to turn. ] (Physiol.) A directive influence exercised by a mass of matter upon growing organs. Encyc. Brit. [ 1913 Webster ]

n. [ Thermo- + Gr. &unr_; to turn. ] (Bot.) The phenomenon of turning towards a source of warmth, seen in the growing parts of some plants. [ 1913 Webster ]

n. [ Gr. troph` a turning, tre`pein to turn + -ism. ] (Physiol.) Modification of the direction of growth, caused by some external influence, such as light; -- sometimes used for motion of an organism toward or away from an external stimulus, more properly called taxis. [ Webster 1913 Suppl. +PJC ]