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Components of the carbon balance in the Sultana vine (Vitis vinifera L.) were examined with emphasis on the autumn, post-harvest, period. The net photosynthetic rate (PN) of leaves decreased from 0.30 to 0.03 mg CO2 m-2 s-1 from January to May (late summer to autumn). Two-thirds of this decline cocurred in the month before leaf fall. This decline in PN as senescence progressed was mainly due to increases in the 'residual', non-gas-phase, resistance to CO2 transfer. 14C-labelled assimilates were shown to move from the leaves to the perennial portions of the vine in both early and late autumn, and this 14C label reappeared in the shoot growth of the following spring. However, the level of carbohydrate reserves in shoots, roots or trunk in the autumn to spring period was not significantly affected by a severe (c. 60%) defoliation in early autumn. This level of defoliation, which the vine is able to tolerate without cumulative effects, occurs where Sultana vines are 'harvest-pruned' as part of the harvesting method of trellis drying.

The absence of boron in the root environment reduced the total linear growth of the radicles of the four dicotyledon and one monocotyledon species studied. After growth for 4 days in a boron-free medium, the growth rate of the maize radicle was comparable to that in a plus-boron medium, whilst the growth of the field bean radicle ceased. The minimum boron requirement for the unrestricted growth of the field bean (Vicia faba val'. minor) radicle over 120 hI' was 0�005 p.p.m. B. Each microgram of boron in this medium evoked a mean radicle elongation of 51 mm.

The CO2 and water vapour fluxes arising from the tops of a plant of A. americana, growing in nutrient solution, were continuously measured at night temperatures of 15, 25, and 36°C, the day temperature being held constant at 25°C.Night temperatures of 36°C inhibited both the large nocturnal uptake of CO2 and the accumulation of titratable acidity. The highest rate of CO2 assimilation by day was about half that of the maximum rate observed by night. From the observed rhythms in transpiration rate, it was inferred that high night temperatures also reversed the usual "inverted" stomatal rhythm found in A. americana and other crassulacean plants. Relative to measurements made at a low night temperature (15°C), high night temperatures induced greater stomatal closure at night and opening during the day. The changes in the gas-exchange pattern induced by high night temperature caused the water use efficiency of this plant to fall to values normally associated with noncrassulacean plants. It is concluded that the normal high water use efficiency of A. americana, and its consequent adaptation to arid climates, is causally associated with a requirement for low night temperatures.