Figure 5.

Operational definition and analysis of branch types. A, Representative examples of the three bifurcation types in primary stalks: splitting into two primary daughters (PPP), into one primary and one nonprimary (PPN), and into two nonprimary daughters (PNN). B, Optimal linear separators for bifurcation types (sample sizes: PPN, 763; PPP, 88; PNN, 155). Functions defining separators were as follows, where DVR is the daughter volume ratio, VP is the volumetric proportion, the ∩ symbol indicates AND Boolean logic, and y is the classification for bifurcation i: y_i = [(PPP = (VP_i > 0.31) ∩ (VP_i > −2.01 × DVR_i + 1.33); PNN = (VP_i < 0.31) ∩ (VP_i < −2.01 × DVR_i + 1.33); PPN = (DVR_i < 0.51) ∩ (−0.65 × DVR_i − 0.02 < VP_i < −2.01 × DVR_i + 1.3)]. C, Log-log frequency distributions of terminal degree (number of terminations) of nonprimary subtrees stemming from PPN (red) and PNN (green) bifurcations. Arrows point to means ± SDs. D, All branch types differ in polarity relative to the vector from the CF origin to the primary tree center of mass (y-axis), whereas values of 1, 0, and −1 would, respectively, indicate directions parallel, orthogonal, and antiparallel to the primary vector. The width of each wedge indicates SD. R, retrograde; P, primary; T, tendril; D, distal. E, Relative branch type contributions to CF size. Error bars indicate SDs (N = 68). F, Tendril and retrograde branches combined and distal branches largely underlie CF bimodality (compare Fig. 3C). The branch type length distributions across path distance are compared with the two modes extracted from the whole trees (gray lines).