Rates of apparent photosynthesis of ears and of the combined flag leaf and sheath and peduncle of Proctor barley grown in pots or in the field were similar to those of Plumage Archer, or slightly smaller when the dimensions of the ear and leaf area of Proctor were less than those of Plumage Archer. The photosynthesis rate of the ear—about 1.0 mg. CO2 per ear per hour—was similar or slightly less than the rate of the flag leaf and sheath and peduncle. These rates of photosynthesis indicated that 40-50 per cent, of the carbohydrate in the grain was provided by photosynthesis in the shoot and about 40 per cent, by photosynthesis in the ear. The total CO2 fixed by the ear was equivalent to about 60 per cent, of the grain weight, 20 per cent, being lost by respiration. Shading the ear underestimated the total amount of CO2 fixed by the ear and decreased dry weight of grain per ear of both Proctor and Plumage Archer by 26 per cent., as in pots. The contribution of ear photosynthesis to yield of grain per acre was greater for Proctor than for Plumage Archer because Proctor had more ears. The rate of apparent photosynthesis per dm.2 of leaves of Proctor was similar to that of Plumage Archer both before and after ear emergence. Before ear emergence, the photosynthesis rate of a particular leaf decreased linearly with time and was slower for lower than for higher leaves on the shoot. Respiration rates per g. dry weight of ears of Proctor and Plumage Archer were similar; in one experiment the leaves of Proctor respired slightly faster than those of Plumage Archer.