Geometric theory predicts bifurcations in minimal wiring cost trees are flat

In the main text (Figure 1) cone angles were computed for complete branches, i.e. for each branch from the bifurcation point to the next bifurcation or terminal point, because these points are morphologically well defined. In Figure S2 we show the same analysis but for bifurcations to the closest point available in the reconstruction. These first points were selected by those who performed each neuron reconstruction and the corresponding segment lengths tend to be quite variable. Though the proportion of planar bifurcations are smaller than in Figure 1, the difference with random bifurcations remains highly significant for all (KS-test, p-value = 10).