The Kinematics of Plant Nutation Reveals a Simple Relation between Curvature and the Orientation of Differential Growth
A. A curve in 3D space (x, y, z). Here, a generalized spiral has been chosen as it provides a nice and simple illustration of an organ curved in different planes in 3D. The curve is described at each point by two vectors, as defined in Fig 2: the tangent and normal to the curve in the plane of the principal direction of curvature, t and c (shown in green and red respectively). The vectors are orthogonal to each others. B. and C. present the projections of the curve onto the (x, z)and (y, z) planes respectively. See S1 Video.