SummaryThe growth response was determined of young tomato plants subjected to wilting treatments of short duration. The experiments were conducted in pots in the glasshouse using Jondaryan loam, and the wilting treatments were at a "moderate" and a "severe" level. Even with the severe treatment, soil water did not fall below the permanent wilting percentage.Both wilting treatments reduced growth during the period of wilting,· but growth rates upon re-watering were greater than for the control plants. There was no indication that this recovery effect was complete at the final harvest.During wilting, a higher stem weight ratio and a lower lamina weight ratio were developed than in the control, and r~lative growth rates and net assimilation rates were depressed in both treatments. After wilting, lamina weight ratios became higher than control, stem weight ratios became lower, and net assimilation rates and relative growth rates rose above control values.These treatment effects may be interpreted as a tendency towards senescence during wilting and a return to a more juvenile condition upon re-watering.It was concluded that the changes in weight ratios were due to modifications of the normal pattern of translocation between plant parts. It was also concluded that the changes occurring in response to the water shortage were initiated relatively early in the drying cycle.The effects of water shortage on the water economy of the plant were also considered. It was found that, whilst there was a high effiCiency of transpiration during wilting, the drastic effects of the water shortage on growth made the greater efficiency of doubtful merit. After wilting, there was no economy in water usage by plants of either of the wilt treatments.

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The effect of phosphorus and sulphur on the initiation and subsequent course of development of effective nodulation was determined for young seedlings of Stylosanthes humilis over the period days 1 1 to 26 from sowing. The plants were inoculated with an effective strain of Rhizobium and grown under controlled conditions in a small amount of nitrogen-deficient soil. Phosphorus had a beneficial effect on the initiation of nodules, which were first detected at day 11 in high-phosphorus plants, but not until day 14 in low. Thereafter, nodule development was greatly enhanced by phosphorus, nodule numbers, volumes and dry weights being increased. Nodule relative growth rates were stimulated from 0 . 3 g/g/day at low phosphorus levels to 0 . 7 g/g/day at high phosphorus levels over days 23-26. The nodules became pink earlier, and developed more rapidly as nitrogen-rich organs, in response to phosphorus. This suggested that from the earliest stages, phosphorus not only promoted the development of an increased mass of nodular tissue but also favoured an effective symbiosis. This enhanced nodule development led to greatly stimulated growth, with increasing amounts of total nitrogen and phosphorus in high-phosphorus plants. The assimilation of nitrogen by the whole plant was increased from 17 mg/g nodule dry weightlday at low to 53 mg/g/day with high phosphorus over days 23-26. Sulphur caused an increase in dry weight, but the response to sulphur mainly occurred late in development and was smaller than the response to phosphorus in the young seedlings of this trial.

The dry weight and water contents data are considered for the individual laminae and petioles of the first eight leaves of tomatoes subjected to a brief period of wilting after they had developed eight easily manipulable leaves. The aim was to obtain a better understanding of the response previously described for the whole plant, by studying the growth of organs which were at various stages of development when treatments were imposed.

The effects over a wide range of interaction of sulfur (S) (5 levels) × phosphorus (P) (5) × nitrogen (N) (6) on nodulation and development of the soybean growing in a nutrient-deficient soil are described for three growth stages: flowering, pod-fill and seed maturity. There were consistent main effects for all three nutrients, but interactions changed from nil at flowering to a few P × N and P × S at pod-fill; and then to predominant P × S at maturity for the principal plant parts. Nodulation was extremely sensitive to levels of nutrient combination, with extremes of nutrient imbalance reducing nodulation almost to zero. Conversely, well-balanced combinations favoured nodulation right through growth until maturity, the best nodulation occurring at high levels of all three nutrients. The yield of seed was not affected by nitrogen supply when sulfur and phosphorus were adequate for an effective nitrogen symbiosis. Introduction