Analysis of PF curvatures. (A) Tracings of all visible PFs from all the KMTs imaged in one algal metaphase spindle. The dark line displays the mean position of these PFs as a function of distance from the MT wall. Error bars indicate SEMs. (B) Average shapes of KMT PFs from PtK₁ cells (data are from McIntosh et al. [2008] whenever PtK₁ numbers are given) and the species described here, all in metaphase. (C) Mean local curvatures, measured as described in Materials and methods, based on circles fit to 10 adjacent points at each position along every PF (inset). KMT PFs from all organisms are compared, colors are as in B. (D) Diagram showing how PF slopes were determined for sorting. (E) Metaphase KMT PFs from a C. reinhardtii metaphase sorted by their slope in the region between the two green vertical lines (see Materials and methods). The lower cluster displays the “ram’s horns,” the upper cluster displays the “intermediate” PFs. There were no “short/blunt” or “extension” PFs in this cell. (F) Fractions of KMT PFs from each organism that fall into the four categories defined in Materials and methods. Comparisons include MTs polymerizing (P) or depolymerizing (D) in vitro, as characterized in McIntosh et al. (2008).