Figure 7.

Pooled inhibition, substrate availability and planar bifurcationA, pooled inhibition. Aa, one generation of branching has occurred, in the horizontal plane. Superimposed on the branching, we show a horizontal cutting plane bisecting the branched structure, and show the distribution of inhibitor H in that plane (blue = low, red = high). Note high levels of pooled inhibition. The next splitting should therefore be driven in the direction perpendicular to the horizontal plane. Ab, by contrast, another horizontal cutting plane, below the plane of branching, shows much lower values of H. Ac, the next generation has begun to split in the vertical plane (arrow), perpendicular to the plane of pooled inhibition. B, planar bifurcation. Tip bifurcation in 3D loses the orthogonal rotation property and forms planar branching when the substrate has restricted availability. In a 3D simulation, when the value of the substrate production rate, c₀, was set to half its value outside the layer marked by the green planes, tip bifurcation could not expand in the vertical direction, and orthogonal rotation was lost.