Structures of averaged plus ends. The program PEET was used to align and average multiple KMT plus ends from each cell (number and kind of MTs plus cell name are given in black for each picture). Averaged structures were sampled with Slicer by cutting a lamina that contained the MT axis at an angle specified in degrees (white in each image). Orientations were selected to show fibrous connections between the averaged MT end and nearby chromatin (arrowheads). (A) Algal KMT shown with the mask used to occlude non-MT features during alignment. (A′) Leftmost is the slice of the reference volume used for MT alignment. Others panels show stages in averaging as more MTs are added. All images are slices at +1° (number in white). Arrowheads indicate a fibril that becomes more distinct with averaging. Bars, 100 nm. (B) Slices from the same averaged algal KMT at different angles. Arrowheads indicate apparent fibrils on all panels. (B′) Analogous images cut at angles shown in white from averaged KMTs from a different metaphase algal cell. (B″) Similar averages of MTs ending far from the chromatin in CrM1. No fibers are seen. (C) Averages from KMTs of one C. elegans metaphase (C) and one anaphase (C′). (C″) Averages of non-KMTs from blastomere spindles.