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The classical problem of chain-packing polarity in native cellulose fibres is approached by electron-diffraction analysis in fibrils of the alga Valonia ventricosa. Meridional reflections up to the 12th layer line were registered and compared with the intensities calculated for one-dimensional parallel and antiparallel models of the structure, projected upon the c-axis. The results are compatible with cellulose molecules packed in parallel fashion, and with a stagger of the central chain with respect to that at the origin of +2,80 or +2,39 A. Some consequences of the parallel structure with regard to the biogenesis of cellulose are discussed. |
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