  Although models of branching in arterial and bronchial trees often predict a
dependence of bifurcation parameters on the scale of the bifurcating vessels,
direct verifications of this dependence with data are uncommon. We compare
measurements of bifurcation parameters in airways and arterial trees of
different mammals as a function of scale to general features predicted by
theoretical models. We find that the size dependence is more complex than
existing theories based solely on energy minimization explain, and suggest
additional factors that may govern the branching at different scales.
