
Figure 8
Delaunay triangulation in a small region around the point s = 15326, which is the last point in a wide sixneighbours ring. The centre of the phyllotactic disc is far away on the left. Red points are common to six triangles, blue points to five triangles and green points to seven triangles. Often it seems that two triangles form a square, but in fact in this sheared square the diagonal which divides it into triangles is slightly shorter than the other one. There are two domains (grains) distinguished by the orientations of the diagonals. In these domains all points are common to six triangles. Between the two domains the defect ring (grain boundary) shows up as a flip of the diagonal orientations, leading to seven, five or sometimes six triangles around a point. Going away from the grain boundary, the triangles become more and more regular. 