Single crystal mata of ultrahigh molecular weight polyethylene (UHMW-PE) have been uniaxially drawn by three techniques: solid-state coextrusion, tensile drawing, and the combination of the two. The drawability and the resultant structure and properties of superdrawn films were found to be sensitive to drawing technique. Tensile drawing was markedly influenced by the coherency of the mats and the draw temperature and rate. Draw ratios (DR) over 200 at 390 O C under controlled rates have been achieved for coherent mats.Effective draw was not possible for less coherent mats and for all drawn at 660 "C. These conventionally drawn films had a single crystal-like texture; those prepared by solid-state extrusion or by two-stage draw showed uniaxial orientation. The mats could be effectively drawn even at 50 "C up to a DR of 35. The most efficient and highest draw has been achieved by first solid-state coextrusion of mats to a low DR of 6, followed by tensile drawing at elevated temperatures. The tensile modulus and strength of such two-stage drawn films increase rapidly with DR in the lower DR range of C150 and approach a constant value of 210-220 and 4.0 GPa, respectively, at higher a DR of 2200-250. With a density of one, these polyethylenes have among the highest and perhaps the highest known specific moduli and strengths, respectively. Such superdrawn, ultrahigh modulus films of UHMW-PE exhibit extremes of chain extension and orientation. The morphological perfection has been assessed by wide-and small-angle X-ray diffraction, density, DSC heat of fusion, etc. The similarities and differences in the structure and drawing of single crystal mats versus gels of UHMW-PE are also discussed.

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Cell division patterning is important to determine body shape in plants. Nuclear auxin signaling mediated by AUXIN RESPONSE FACTOR (ARF) transcription factors affects plant growth and development through regulation of cell division, elongation and differentiation. The evolutionary origin of the ARF-mediated pathway dates back to at least the common ancestor of bryophytes and other land plants. The liverwort Marchantia polymorpha has three phylogenetically distinct ARFs: MpARF1, the sole 'activator' ARF; and MpARF2 and MpARF3, two 'repressor' ARFs. Genetic screens for auxin-resistant mutants revealed that loss of MpARF1 function conferred auxin insensitivity. Mparf1 mutants showed reduced auxin-inducible gene expression and various developmental defects, including thallus twisting and gemma malformation. We further investigated the role of MpARF1 in gemma development, which is traceable at the cellular level. In wild-type plants, a gemma initial first undergoes several transverse divisions to generate a single-celled stalk and a gemma proper, followed by rather synchronous longitudinal divisions in the latter. Mparf1 mutants often contained multicelled stalks and showed defects in the execution and timing of the longitudinal divisions. While wild-type gemmae finally generate two meristem notches, Mparf1 gemmae displayed various numbers of ectopic meristems. These results suggest that MpARF1 regulates formative cell divisions and axis formation through auxin responses. The mechanism for activator ARF regulation of pattern formation may be shared in land plants and therefore important for the general acquisition of three-dimensional body plans.

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