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Abscisic acid (ABA) was synthesised in dehydrating leaves and roots of willow (<I>Salix dasyclados</I>) and exogenous ABA in the xylem stream was shown to cause decreases in stomatal conductance. A transient decrease in leaf water potential occurred if water was entirely withheld from roots on one side of a willow plant. This was avoided if roots from all sides of the plant were watered and only root tips were allowed to dehydrate. Partial stomatal closure and decreased leaf extension rate then occurred without any initial perturbation in leaf water potential or leaf ABA. The drying event was associated with an increased content of ABA in root tips and xylem sap. The effects were reversible on either rewatering or excision of the affected root tips. It was concluded that partial dehydration of root tips caused partial stomatal closure and decreased leaf extension, and that changes in the ABA content of root tips and the xylem sap were consistent with a possible causal role for root-sourced ABA in the regulation of leaf physiology in response to root water deficit. Stem-girdling experiments indicated that a major pathway of ABA transport, between leaves on different stems in the shoot system, was in the phloem, without an apparent involvement of transport in the xylem. Damage to the shoot apex caused an increase in stomatal conductance. This was associated with a decreased content of ABA in the xylem sap and in fully extended leaves. It is suggested that these changes may have been associated with a possible import of ABA from mature leaves into the growth sites of axillary shoots. Results are discussed within the context of water deficit and the growth and survival of individual stems in a willow plantation.

Within close packed kiln dried Sitka spruce timber a disfiguring sapwood stain, caused by <I>Ophiostoma piceae</I>, frequently developed. Spoilage was investigated through research into nutritional status, moisture content and wettability of Sitka spruce timber, physical conditions within stacks of timber, moisture and nutritional requirements of <I>O. piceae</I> and infection of timber by <I>O. piceae</I>. Recommendations to minimise spoilage of kiln dried timber were made. Carbon and nitrogen compounds abundant in softwood did not result in greater growth than others. Cellulose and lignin were not degraded; <I>O. piceae</I> was unable to grow into wood. Saturated atmospheres of monoterpenes reduced growth rate, pigmentation and coremia formation on agar. Kiln dried batten surfaces contained 18% glucose, 8 times higher than green or air dried timber. However, growth was not nutritionally limited on air dried compared to kiln dried wood. The carbon/nitrogen ratio of kiln dried battens (4500:1) was 3 times higher than green timber and 9 times higher than air dried timber. The minimum relative humidity for growth of <I>O. piceae</I> was 93%, at which the moisture content of Sitka spruce sapwood was 21%. Stain coverage increased from zero at a batten moisture content of 15%, to 10% cover at 25% moisture content. Partially air dried timber developed greater stain coverage than kiln dried timber stored in similar pack types. Stain development was greater in summer than winter, when it was limited by temperature. Maximum mean batten stain cover (32%) developed in close packed wrapped partially air dried timber during warm and wet weather conditions. Kiln dried stickered timber only developed a lower mean batten surface moisture content than close packed timber during the summer. Moisture content of individual rows of battens within packs stored in the sawmill yard developed different moisture contents and stain coverage. Greater staining developed on rows with higher moisture content, which tended to be located toward the upper surfaces of packs exposed to percolating rainwater.

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The results of a theoretical and experimental investigation into the drying of wheat and barley in two stages with an intervening rest period are presented. The reduction in drying time, excluding rest period, has been determined in comparison with the conventional continuous drying for various drying requirements. The effect of airflow rate and the temperature difference between grain and air on the reduction in moisture content and the time required to cool the grain during dryeration is also included. The moisture diffusion equation was solved numerically assuming a spherical grain. The variable grid spacing, Crank-Nicolson approximation technique and the Gauss-Seidel iterative procedure was employed. The theoretical predictions were compared with experimental results. The drying and resting was performed on a thin layer at a temperature of 60°C. An automatic micro-computer based system was developed to record and store the experimental data. The results indicate that the moisture redistribution during resting is well advanced after a period of two hours for wheat and one hour for barley. The extent of redistribution was measured by the increase in drying rate observed as the rest period was extended. An optimum moisture content for commencing resting is specified, which is a function of initial, final and equilibrium moisture contents. This optimum was chosen to minimise the actual drying time. There is good agreement between the theoreticaaand experimental predictions. It was found that the incorporation of a surface resistance into the diffusion model improves the description of the experimental results. The results enable a drying strategy to be specified that reduces the actual drying time by as much as 39%. - iv For dryeration experiments, the grains pre-heated to different temperatures were put into a well insulated aluminium cylinder and aerated at various airflow rates. An airflow rate of about 60-120 m3/hr/m3 of grain was found to be optimum. The moisture reduction during cooling was observed to be 0.65 to 0.78% (db) per 10°C temperature difference. It was noticed that moisture reduction also depends on initial moisture content of the grain. The practical implications of two-stage drying are discussed.

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No description available.