Variation existed between plants of the lucerne (Medicago sativa L.) cultivar CUF 101 for dry matter production, shoot number and length, and leaf damage when grown for 70 days under 250 mM NaCl (15 h photoperiod, 20�C day, 10�C night). Salt tolerance evaluation using the criteria percentage leaf damage (percentage of total number of leaves with complete or partial necrosis) and length of the main shoot, isolated plants which showed salt tolerance of reasonably high heritability (h2=0.41). Two generations of recurrent selection for tolerance significantly increased the mean population tolerance without decreasing production under non-saline conditions. While both sodium and chloride concentrations of the shoot were lower in the tolerant than in less tolerant plants, chloride was more closely associated with salt tolerance than sodium. Sodium and chloride concentrations in the roots did not vary with the level of salt tolerance. No association of shoot and root potassium concentration with tolerance was evident. Selection for salt tolerance in lucerne plants using percentage leaf damage of less than 10% as the main criterion should give a rapid response to selection. The efficiency of selection may be increased if selection is based on the efficiency of chloride exclusion from the shoots and/or the level of chloride tolerated by the shoots prior to leaf damage becoming evident.

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The relationship between leaf resistance to water vapour diffusion and each of the factors leaf water potential, light intensity and leaf temperature was determined for leaves on seedling apple trees (Malus sylvesiris Mill. cv. Granny Smith) in the laboratory. Leaf cuticular resistance was also determined and transpiration was measured on attached leaves for a range of conditions.Leaf resistance was shown to be independent of water potential until potential fell below -19 bars after which leaf resistance increased rapidly. Exposure of leaves to CO2 free air extended the range for which resistance was independent of water potential to -30 bars.The light requirement for minimum leaf resistance was 10 to 20 W m"^ and at light intensities exceeding these, leaf resistance was unaffected by light intensity.Optimum leaf temperature for minimum diffusion resistance was 23 ± 2°C. The rate of change measured in leaf resistance in leaves given a sudden change in leaf temperature increased as the magnitude of the temperature change increased. For a sudden change of 1°C in leaf temperature, diffusion resistance changed at a rate of 0.01 s cm"' min ' whilst for a 9°C leaf temperature change, diffusion resistance changed at a rate of O.

A change occurs in the relationship between xylem water potential (Ψx) measured with the pressure chamber and leaf water potential ((Ψw)) when a period of post-excision water loss is allowed before measurement of (Ψx) and (Ψx). When this occurs, water stress is over-estimated by the pressure chamber measurement. Over the same period of water loss, cavitation vibrations have been detected acoustically in excised leaves. It is suggested that the measurement of (Ψx) is affected by emptying of some of the xylem vessels due to cavitation. This would require that additional pressure be applied to a leaf in the pressure chamber in order to measure (Ψx).

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