NUTATION (in Plants). The bending move ments executed by organs of plants, such as stems, leaves. roots, etc., by which the part is inclined successively in various directions. Nutations are due to the unequal rate of growth of different sides of the organ, an inequality which, as far as is known at present. is de pendent upon internal (unknown) causes, and is not called forth by the action of external stimuli. See IRRITABILITY.
Simple notation occurs in dorsiventral organs. such as that leaves, both foliage and floral. The movements are only in one plane. being dependent upon the unequal growth of the opposite sides. When young the growth of the foliage leaves is most rapid upon their outer (dorsal) face, in consequence of which the leaf applies itself to the axis, arches over the apex, and with its neigh bers forms a compact bud. Later. growth be c•onmes more rapid on the inner (ventral) face. the bud opens, and the leaves straighten out. Similar inequality of growth, but more sharply localized, leads to the folding and rolling of the leaf in the bud. (See Vernat ion, under Bun.) Like movements of radial organs, such as stems, cylindrical leaves, and roots. have been termed eireumnutation or revolving, notation, to distinguish them from the simple notation of dorsiventral organs. 'When any plant is in
vigorous growth the axis rarely grows in length uniformly on all sides. The side on which growth is Most rapid will push the apex over toward the side on which growth is less rapid. If the region of more rapid growth changes, shifting around the axis, the tip will he inclined successively to all points of the compass. and with its simul taneous upward growth will describe a spiral; but since the rate of growth is not uniform at •-necessive intervals, the path described will be a cry irregular spiral. A path of this kind, re duced to a plane, is shown in the accompanying figure.
Movements quite similar to those above de scribed are called forth in plant organs as re spouses to external stimuli. Thus twining plants exhibit both true notation and notation due to a geotropic sensitiveness. (Sec (4Eontoetsm IN PLANTS.) Changes in temperature cause flowers to open or close by movements which resemble the simple notation of dursiventral organs. Thus the tulip, crocus, and other vernal flowers are very sensitive to ehanges in temperature. The latter can perceive a change of 0.5' C., and will respond to a change of 20° C. in two minutes.