Fig. 6. The progressive increase of the cell density correlated successively with the formation of an apterium, a semi-apterium and a pteryla. (A) The pteryla was characterized by a regular pattern. (B,C) The decrease of cell density (q) to 0.2 (B) and 0.12 (C) led, respectively, to an irregular pattern at the boundary of the pteryla and the semi-apteria. (D) The switch from spot formation to a glabrous region implicated only a small difference in cell density (q=0.12 versus q=0.11).