Varietal Differences in Photosynthesis of Ears and Leaves of Barley

Rates of apparent photosynthesis of ears and of the combinedflag leaf and sheath and peduncle of Proctor barley grown inpots or in the field were similar to those of Plumage Archer,or slightly smaller when the dimensions of the ear and leafarea of Proctor were less than those of Plumage Archer. Thephotosynthesis rate of the ear—about 1.0 mg. CO₂ per earper hour—was similar or slightly less than the rate ofthe flag leaf and sheath and peduncle. These rates of photosynthesisindicated that 40-50 per cent, of the carbohydrate in the grainwas provided by photosynthesis in the shoot and about 40 percent, by photosynthesis in the ear. The total CO₂ fixed by theear was equivalent to about 60 per cent, of the grain weight,20 per cent, being lost by respiration. Shading the ear underestimatedthe total amount of CO₂ fixed by the ear and decreased dry weightof grain per ear of both Proctor and Plumage Archer by 26 percent., as in pots. The contribution of ear photosynthesis toyield of grain per acre was greater for Proctor than for PlumageArcher because Proctor had more ears. The rate of apparent photosynthesis per dm.² of leaves of Proctorwas similar to that of Plumage Archer both before and afterear emergence. Before ear emergence, the photosynthesis rateof a particular leaf decreased linearly with time and was slowerfor lower than for higher leaves on the shoot. Respiration ratesper g. dry weight of ears of Proctor and Plumage Archer weresimilar; in one experiment the leaves of Proctor respired slightlyfaster than those of Plumage Archer.