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Uptake of [3H]leucine by leaf fragments and roots from Lycopersicon esculentum (domestic tomato) and L. hirsutum (a wild tomato) was compared. Uptake of amino acids was affected by metabolic inhibitors and temperature. The L. esculentum cultivars studied, Rutgers and PI.341985, showed similar uptake rates above 12°C. After preincubation at the uptake temperatures below 12°C, the Q10 for uptake for PI.341985 was about 25 while for Rutgers it was about 125. The temperature response was similar for root and leaf material and for material grown at different temperatures (24/18 and 15/5°C). The temperature response of the uptake by leaf fragments of the wild races of L. hirsutum was related to the altitude of origin. The race from the highest altitude (3100 m) showed little change in slope in a plot of tog uptake rate versus temperature over the range 4-20°C. The race from the lowest altitude (30 m) resembled the cultivars of L. esculentum in its response to temperature and showed an increasing slope below 10°C. The race of L. hirsutum from 1500 m responded to temperature in an intermediate fashion. It is concluded that the decrease in the rate of uptake of amino acids during incubation at chilling temperatures can be related to genetic adaptation to the temperature of the native habitat and chilling resistance of the variety of Lycopersicon used.

The effect of planting dates between September 30 and November 30 on the yield and some fibre properties of two cotton cultivars has been studied over three seasons. The yield of the commercial cultivar (Deltapine Smoothleaf) fell by an average of 20 kg ha-1 day-1 delay in planting after October 20, earlier planting dates having equal yields, producing a plateau effect. The yield of an early maturing cultivar (Short Sympodial) fell linearly by 11 kg ha-1 day-1 delay in planting. Planting dates after mid-October had an adverse effect on micronaire in the commercial cultivar, but lint length and strength were not affected. Thus maximum yield and micronaire for plantings after mid-October came from the early cultivar. Tolerance to low temperature is an important factor in cultivar earliness, and accounts for the performance of Short Sympodial in these experiments. The number of days from first flower to first frost was as reliable as growing degree days in explaining yield variation within a cultivar