Figure 10. Widening of the Y-stalk is required for tip splitting.

(a) The first activator peak emerges at the growing tip. (b) forward migration of the leading activator peak produces elongation of the Y-stalk. (c) the leading activator splits into two daughter peaks as the Y-stalk becomes wider, shown by the arrow. (d) each of the daughter activator peaks, from the 1^st generation splitting, becomes the leading activator peak of the newly formed stalks. (e) 2^nd generation of tip splitting occurs when the daughter stalks get wide enough, shown by the arrow. (f) each of the granddaughter activator peaks becomes the leading activator peaks of the newly formed stalks, and migrates forward. Parameters:  = 0.002,  = 0.16,  = 0.04,  = 0.03,  = 0.0001,  = 0.02,  = 0.02,  = 1.0,  = 0.008,  = 0.1,  = 10,  = 0.02,  = 0.26,  = 0.06.