In this paper, we present a following theory on th e growth of the plants twinning along the supporting rod. "A Twinning plant has a special propensity for climbing the support, regardless to its thickness, with a definite curvature." The formula obtained is h^2/4πr = constant = ρ Where h is the pitch of the spiral, r the radius of the support. The theory was confirmed experimentally with following plants. (snip)