Figure 3. Periodic activator peaks along the Y-stalk determines pre branch sites.

(a) the leading activator peak emerges at the growing tip, marked by *. (b) Forward migration of the leading activator peak produces the elongation of the Y-stalk. When enough space is created behind the leading activator peak, a new activator peak will be induced right behind it, marked by double arrow. (c–f) After several rounds of peak insertion, activator peaks line up along the Y-stalk. (g, h) later on, these activator peaks migrate out in the transversal direction, each of which becomes the leading activator peak of the newly formed side branches, marked by *. Parameters:  = 0.002,  = 0.16,  = 0.04,  = 0.03,  = 0.0001,  = 0.02,  = 0.02,  = 0.0025,  = 0.008,  = 0.1,  = 10,  = 0.02,  = 0.26,  = 0.06.