Angular sampling of the 3D structure of a growing MT end. (A) Nine slices through the end of an MT from the anaphase B interzone in a PtK₂ cell. All images contain the MT axis, but the orientation of the plane of sampling the 3D volume was changed to display flaring PFs. Red crosses mark the origins of the coordinate systems used. (B) The same images showing the angles at which the slices were taken and graphic objects drawn by hand on the image data. Red x's mark the tips of the graphic traces that represent the PFs. (C and D) Two orthogonal views of the graphic objects drawn on this MT end. Bars, 50 nm. (E) 346 PFs traced on the plus ends of 42 elongating IPMTs from four S. pombe (Pombe) cells in anaphase B that were cryoimmobilized by high-pressure freezing (HPF) and then prepared for EM. (F) The same traces after smoothing with a quadratic LOESS filter. (G) LOESS-filtered traces from 399 PFs from the plus ends of 45 IPMTs identified in four anaphase S. pombe cells cryoimmobilized by plunge freezing and then prepared for EM. (H) Means and SEMs for positions traced along all PFs from these two datasets to compare mean PF shapes after two methods of freezing.