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SUMMARYThe pattern of leaf growth and death was followed in stands of cowpea grown in the field at Ibadan, Nigeria. Temperature affected this pattern. Leaf area index increased quicker and leaf death started sooner during warm seasons. Individual leaves died while pods at the same node were filling. The rate of leaf appearance increased with temperature and the duration of expansion of individual leaves decreased so that a constant number of leaves were expanding at one time. The mean rate of expansion of individual leaves increased with temperature proportionately more than the duration decreased, hence final leaf size increased with temperature. Base temperatures for leaf appearance and leaf expansion were 16 and 20 °C respectively.

The CO 2 exchange of leaves, pods and peduncles was measured in cowpea crops grown at Ibadan, Nigeria, using a portable infra-red gas analysis system. Most leaves had maximum rates of photosynthesis (P m ) of about 1-4 mg CO 2 /m 2 /sec and maintained this value for 20 days from full expansion. Early leaves had slightly slower rates. P m decreased when leaf temperature exceeded 35 °C. The maximum efficiency of photosynthesis, e m , was about 2 g CO 2 /E (0-045 mol CO 2 /E). e m decreased with temperature for leaves, but increased for pods. The latter response probably results from the effect of the high CO 2 concentrations within the pod on the ribulose disphosphate carboxylation reaction. Water shortage reduced P m but not e m . Pods and peduncles had a slightly negative CO, exchange rate at light saturation but this was considerably less than the rate of CO a evolution in the dark. a n c e °f *h e m a i n environmental factors, light, water and temperature, on rates of photosynthesis There have been few field measurements of photo-in the field. A second aim was to determine how synthesis in the tropics, particularly of C 3 plants, photosynthesis rates of leaves varied with age and In this paper we report measurements of photo-position. A third aim was to measure the rates of synthesis made in crops of cowpea (Vigna unguicu-photosynthesis of pods and peduncles. Photolata) in Nigeria. The growth and development of synthesis by such organs has rarely been measured these crops has been described (Littleton, Dennett, in the field. . Apparatus for the measure-MATERIALS AND METHODS ment of rates of photosynthesis in the field has usually lacked ways of controlling the environment. Gr0 P husbandry Littleton (1971) developed a system with effective Crops of an erect, almost determinate cultivar of temperature control. The measurements described cowpea, TVu 4552, were grown at the experimental here were made with a refined version of that farm of the International Institute for Tropical system, capable of holding leaf temperatures con-Agriculture (IITA), Ibadan. All crops were hand stant in the climate of the humid tropics.planted at a spacing of 0-25 x 0-25 m. Cultural deThe first aim was to establish the relative import-tails and climatic records for the crops have been •

SUMMARYThe pattern of dry weight accumulation and partition of cowpea crops grown in Nigeria is described. For the first 50 days, increase in dry matter was proportional to intercepted radiation. Differences in dry weight between crops were due equally to variations in incident solar radiation, the fraction of this radiation intercepted, and the efficiency with which it was used. The variation in total pod weight from 206 to 312 g/ma resulted from differences in number of pods, mean pod weight being constant. The pod weight ratio was relatively constant and there was a strong relationship between final number of pods and total plant dry weight.

SUMMARY The gas exchange of barley ears and awns was measured in the field using a gas analysis system and a diffusion porometer. Awn stomatal resistance decreased with increasing irradiance but to a smaller extent than leaf stomatal resistance. Measurements on ears immediately before and after successively removing awns showed that awn transpiration and photosynthesis were proportional to awn area and that awns accounted for 73% of transpiration by the ear. Although the maximum rates of photosynthesis of which awns were capable declined with age, awns accounted for 80–115% of the net CO2 uptake of complete ears because the ears‐less‐awns could respire more CO2 than they absorbed. Ear photosynthesis accounted for 52% of the weekly increment in ear dry weight after ear emergence, but 5 weeks later photosynthesis by the ear balanced respiration. Overall photosynthesis by the ear accounted for 35 % of its final weight. Differences in the light response curves of leaves and ears can be fully accounted for by the different relationships between stomatal resistance and irradiance of the two organs.