Microscopic Structure of the Cotton Fiber

During the examination of cotton fibers that had received vari ous chemical treatments, a number of observations pertaining to the structural details of the fiber were made. Those phenomena which appeared to be new were investigated in detail. In addition, experiments described by earlier investigators were repeated in order to have a better composite picture of the structure of the fiber.

The cell wall of a cotton fiber consists of a primary and a sec ondary wall. The latter, which comprises the bulk of the fiber, con sists of innumerable spirally oriented cellulose fibrils enclosed by a winding which also makes a spiral, but in the opposite direction from the former. Both the winding and the fibrils reverse their direction at frequent intervals along the axis of the fiber, their points of reversal being coincident. The secondary wall is en closed by a thin primary wall. The latter is made up of fine criss crossing strands of cellulose embedded in a membrane consisting principally of wax and pectic substance. The lumen also contains wax and pectic materials, plus various amounts of degenerated pro toplasm.

When cotton fibers are swollen under certain conditions a lamel late structure is discernible in the secondary wall. The number of these lamellae increases with the age of the fiber.

On treatment of cotton fibers with cuprammonium hydroxide reagent, the cellulose dissolves, leaving residues which vary in amount and in structure, depending upon the extent of purification of the fibers. The residue from raw and from dewaxed fibers con sists of fragments of the primary wall, and of a lesser amount of material from the lumen. The behavior of the fibers in the reagent depends in part on their maturity. Immature fibers containing only small amounts of cellulose swell relatively little in the reagent and the undissolved wax and pectic materials maintain the original tubular shape of the primary wall. When older fibers are given the same treatment they swell abruptly, thereby causing the primary wall to break in many places, giving rise to "balloons."

Irregular swelling along the fiber axis, which results in the formation of balloons, appears to be dependent in part on the orien tation of the fibrils, and in part on the constricting influences of the winding and of the primary wall.