Accessibility and Lateral Order Distribution of the Cellulose in the Developing Cotton Fiber1

Cotton fibers from bolls harvested at 5-day intervals beginning at 20 days after flowering and ending at 50 days ( when the bolls had opened on the plant) 'were preserved in three ways for study in the never-dned state. Preservation was accom plished in 70% aqueous ethanol, 50% aqueous dioxane, and by freezing. Measurements of iodine sorption, red-green ("differential") dye uptake, and liquid-phase deuteration rehydrogenation gave different kinds of estimates of accessibility. These data were interpreted as indicating a relatively open structure during the 20- to 30-day period of growth, and a consolidation of the cellulosic component of the cell wall during the subsequent period of wall-thickening (35 to 45 days after flowering). There was only a small change in magnitude of these data upon boll opening. The leveling-off D.P. was nearly constant from the 30th to the 45th day, but showed a slight decrease after boll opening. Lateral order distribution was assessed by treatment with sodium hydroxide solu tions of increasing concentrations, followed by moisture sorption measurements and x-ray evaluation of extent of lattice transformation. The data indicated perhaps a slight increase in lateral order from 20 to 30 days after flowering, then a leveling-off from 30 to 45 days and a small increase upon boll opening at 50 days. These data are interpreted as indicating that the high crystallinity of the mature cotton fiber does not suddenly appear when the fiber first dries as the boll opens, but begins to develop concurrently with the deposition of cellulose during the period of wall thickening, and reaches the final high value by crystallization of an additional small fraction of cellulose upon initial drying.