• Volume 85, Issue 4

      April 1977,   pages  173-268

    • Natural radioactivity and geochemical processes in the marine environment of the west coast of India

      L U Joshi A K Ganguly

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      In studies related to the geochemistry of thorium and uranium, it was observed that the disequilibrium between Th232 and Th228 and between U238 and U234 exists on the surface of the labile organic layer of the sediment particles and as the surface organic matter is removed the core of the particles show equilibrium activities. The studies related to sedimentation and geochemistry of elements in coastal waters, it is important to recognise the physicochemical equilibrium between labile chemical species present on the particle surface and the chemical species in the ambient medium.

      The thickness of the labile organic layer on the sediment particles has been calculated and found to be in the range of 2·5×10−6 cm to 10·0×10−6 cm. The values are comparable to the values obtained by Electron Microscopy Method.

    • Relationship between preformed/post-infectional antifungal substances in leaves ofPanicum repens L. and compatibility withPyricularia spp.

      A Hilda S Suryanarayanan

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      Preformed and post-infectional antifungal substances appear to be involved in the compatibility ofPyricularia spp. withPanicum repens L. Diffusates and extracts of ‘uninoculated’ or leaves inoculated with the compatible or incompatible isolates showed antifungal activity. However, the antifungal activity was found to be localized. Antifungal activity was also evident in mechanically injured leaves or leaves treated to cell free germination fluid of an incompatible isolate. The presence of preformed and post-infectional protectants was confirmed by thin-layer chromatography. Post-infectional protectants appeared earlier in leaves inoculated with the incompatible isolate than in leaves inoculated with the compatible isolate. The incompatible isolate was more sensitive than the compatible isolate to preformed and post-infectional protectan’s.

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