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Physiology and Biochemistry

Formation and Properties of Wetwood in White Fir. J. J. Worrall, Research assistant, Department of Plant Pathology, University of California, Berkeley 94720; J. R. Parmeter, Jr., professor, Department of Plant Pathology, University of California, Berkeley 94720. Phytopathology 72:1209-1212. Accepted for publication 15 January 1982. Copyright 1982 The American Phytopathological Society. DOI: 10.1094/Phyto-72-1209.

In white fir, wetwood is the usual condition of the heartwood. It is characterized by a moisture content generally equal to or greater than that of sapwood, a slightly lower pH, and a red-brown color. Ray parenchyma is alive and contains starch in the dry-appearing transition zone; at the wetwood border, however, nuclei disintegrate, starch disappears, and phenols accumulate. Osmotic potentials (φπ) are consistently lower than those in sapwood. Analyses of sapwood and wetwood indicate a selective accumulation of K, Ca, and organic acids in wetwood. The elevated levels of solutes account for much of the observed decrease in φπ. The data support an osmotic hypothesis to account for accumulation of water in wetwood.