Analysis of measurements of absorbed radiation and leaf area indices of wheat and barley crops showed that throughout most of growth the fraction of absorbed solar radiation could be described by a simple exponential equation.For several of these crops grown under a wide range of weather and husbandry at Sutton Bonington and Rothamsted, 2-weekly values of crop growth rate (C) were closely related to radiation absorbed until ear emergence and about 3-0 g of dry matter (D.M.) were produced by each MJ of photosynthetically active radiation (PAR) absorbed. Final crop weight was closely related to total PAR absorbed during growth (£4); on average about 2-2 g D.M. were produced per MJ absorbed, equivalent to a growth efficiency (e 0 ) of approximately 3-9%. Unfertilized and drought-stressed crops had a smaller e 0 .The fraction of total crop D.M. harvested as grain (harvest index) varied more for wheat than for barley. Calculations of a maximum realizable grain yield made using the largest values of e 0 and SA for the crops measured and assuming a harvest index of 0-53 (achieved in an experimental crop) showed a grain D.M. yield of 10-3 t D.M./ha to be possible. To achieve such a yield would require full crop cover from the beginning of April until the end of July in a typical English growing season. INTRODUCTIONCROPS, SITES AND SEASONS

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PTB is as effective as standard sutures for wound closure in porcine skin in terms of cosmetic outcomes and safety.

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A scheme was developed to describe how the rate at which apical primordia are initiated in cereals depends on temperature and photoperiod. It was used to analyse initiation in field crops of winter wheat (Triticum aestivum L., cv. Maris Huntsman).For the initiation of leaves and spikelets, a straightforward linear regression of initiation rate R against mean air temperature (T a ) gave base temperatures (T 6 ) close to 0 °C for leaves and for spikelets. However, initiation rate was also correlated with mean photoperiod (P) and base photoperiods (P t ) of -0-5 h and 4h were established for leaf and spikelet initiation. When R was correlated with the index (T -T t ) (P -P b ), r 2 was 0-62 for both leaves and spikelets.

Main-stem apical development and its inter-relations with other aspects of plant morphology were studied in seven field crops of winter wheat (Triticum aestivum L., cv. Maris Huntsman).Apical primordia were produced slowly in autumn and winter, then faster in spring as the weather became warmer. Spikelets were initiated about three times as fast as leaves. Leaf initiation ended at around the time that tiller bud initiation stopped. Apical dome length and diameter both increased during leaf initiation, reached a maximum at double ridges and then decreased. Double ridges appeared when very nearly 50 % (range 49-52 %) of the final number of spikelets was present. Spikelet initiation ended a few days after the first florets were initiated and when stem extension began, but usually before the stem apex rose above the soil. Floret initiation finished at about the time that the flag leaf appeared. Throughout tillering there was a strong association between tiller emergence and leaf appearance.There were considerable differences between seasons in the timing of developmental events on the apices of main stems, but a difference in sowing date of 5 months was reduced to little more than 1 month in the timing of anthesis and the maximum numbers of organs varied only slightly with sowing date.