Figure 2.

Micrographs showing the onset and effects of fiber bundling. A to E and G, Cryo-FE-SEM observations of fiber within the boll in the “as living” state, showing twisting fiber tips (A), material fusing adjacent fibers (double arrow; B), material (arrow) connecting the tip of one fiber to another fiber below (C), fiber bundles adopting curving paths (D), and a site on the outside of the fiber mass (arrow) where fiber tips have turned inward toward the seed (E). F, Specialized paraffin embedding of intact locules revealed organized fiber around each developing ovule. The left panel shows a cross-section of a 10-DPA ovule (densely stained) surrounded by a packet of its own fiber (gray halo). The distinct outer boundary of the “fiber packet” was consistently observed. The right panel shows a higher magnification view of a cross-sectioned fiber bundle within the fiber packet, even though the extended specimen preparation for paraffin embedding resulted in some fiber separation (see Supplemental Fig. S4 for additional views). G, From 5 DPA onward, a mass of tightly packed fiber bundles in meandering patterns was closely appressed to the boll wall. Ages of fiber (DPA) are as follows: A and D, 2; B and C, 6; E, 4; F, 10; and G, 5. Bars = 50 μm (A), 9 μm (B), 5 μm (C), 250 μm (D and G), 100 μm (E and F, right), and 750 μm (F, left).