The increase in dry weight of wheat kernels after flowering accelerated slightly for 14 days, was steady for 10 days, then fell off gradually to zero in about 14 days more, when the kernels weighed 32 gm. per 1,000. At this stage they contained 58 to 60% dry matter, a critical point marking the practically complete cessation of chemical changes.The weight of nitrogen increased steadily to about 1 gm. per 1,000 kernels at the critical stage. Respiration losses of carbon, before and after harvest, appear to account largely for the changes in the percentage nitrogen in the kernels. The ratio of nitrogenous to non-nitrogenous material moved into the endosperm seems to have been nearly constant throughout the main developmental period.Ammonia nitrogen first increased to a maximum of 4.8 mg. per 1,000 kernels, then decreased to negligible proportions at the critical stage Salt-soluble nitrogen in fresh kernels decreased from an initial value of 75% of the total nitrogen to 22% at the critical stage, when a little more than one-third of it was non-protein. Drying the kernels before analysis changed the percentage composition, owing to respiration and synthesis, by an amount varying with rate and conditions of drying.Frost had no effect on the ash content of the kernels. Four degrees of frost (28° F.) had no effect on the per cent total, salt-soluble or non-protein nitrogen, but 8, 10 and 14 degrees, in cuttings before the critical stage, in both the gram and the flour milled from it reduced the per cent total nitrogen an effect ascribed to slowing up of respiration, and increased the per cent of the fractions, ascribed to checking of synthesisYields of washed gluten from the control samples were about the same at all stages, but physical properties did not attain maximum quality before the critical stage. Four degrees of frost did not affect yield, but reduced quality in cuttings before the critical stage. More severe frost reduced both yield and quality in immature samples, the effect of the heaviest frost on quality persisting to full maturityBoth reducing and invert sugar percentages declined m early stages of development. Frost did not affect invert sugar content, but 8, 10 and 14 degrees increased reducing sugars in flours from grain cut before the critical stage. This is ascribed partly to increased enzyme activity, as indicated by greater maltose production, and partly to slowing of respiration by frost injury. Gain in kernel weight by translocation after cutting took place in immature check samples but not in heavily frozen samples. Respiration losses in the stook were calculated to be about twice as great from the checks as from the heavily frozen samples.
Starch Synthesis and Changes in Uridine Diphosphorlase in the Developing Wheat Grain