The base temperature (T b) and thermal time (Tt) requirements for germination and emergence of temperate herbage species were defined using a linear model of development rate against temperature. A T b of 4°C was found for all species. The Tt requirement for germination was lower for legume than grass species and generally lowest for small seeded species. The poor relationship (R 2 = 0.42) between Tt requirements for germination and 50% field emergence indicated that germination results could not be extrapolated to predict the rate of field emergence. The Tt for 50% field emergence was highest for the small-seeded grass species cocksfoot (220°Cd) and timothy (200°Cd). The times (days and Tt) for emergence of white clover and perennial ryegrass were similar from five autumn sowing dates but 57 days after sowing on 21 March 1996 ryegrass seedlings were 12 times heavier. The implication of these results for establishment of pasture mixtures is discussed together with the need for accurate measurement of soil temperatures to assist the prediction of field emergence.

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Long-range ferromagnetic coupling occurs in several dilute solid-solution alloys of the ferromagnetic transition elements in Pd or Pt. New measurements of magnetic moments and Curie temperatures of PdFe, PtFe, PtCo, and PdNi alloys are reported, and previous work on these and some of the more general properties of these alloys are briefly reviewed. Also, ferromagnetism occurs in dilute PdGd solid solutions. Dilute solutions of iron in gold are ferromagnetic, although below about 10% of Fe there seems to be no homogeneous bulk ferromagnetism.

SUMMARYGrain growth and final weight per grain were measured in 12 genotypes of spring barley, the parents and progeny of two six-row × two-row crosses. Weight of carpels or grains from node 10 on the main shoot ear was measured from shortly after meiosis until grains were at maximum dry weight. Similar measurements were made at representative node positions along the ear of Proctor and of Midas spring barley cultivars.From about 10 days after anthesis grains grew at a constant rate for about 3 weeks. Amongst genotypes growth rate of the median grain ranged from 1·4 to 2'2 mg/day and there was a very highly significant positive correlation between growth rate and final grain weight. A similar relationship was found among grain positions on the ear. For about 10 days after anthesis growth was exponential and although relative growth rate did not differ between genotypes or grain positions there was a highly significant difference between caryopsis weights during this phase. There were significant correlations between final grain weight and carpel weight at anthesis and between final grain weight and husk weight at anthesis. In the period between meiosis and anthesis growth was exponential and the relative growth rate did not differ between genotypes or node positions on the ear. There were significant differences between carpel weights during this phase. Carpel weight at anthesis and carpel linear dimensions at meiosis were correlated.These data suggest that the initial size of carpel is an important factor in determining growth rate and potential grain weight. Potential grain size in barley may be determined by physical limitations imposed by the lemma and palea or may be causally related to the size of the carpel. The relative size of the carpel is determined by the time of meiosis and potential size may also be affected by pre-anthesis conditions.

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