A few potato lone, such as A6948-4, had higher rates ofphotosynthesis in the f than the Russet Burbank and were able to maintain higher rates not only dring miday but also in the early mornng and late evning For many species, more than 95% of the plant dry weight is derived from photosynthetically fixed CO2 (17). Many physiologists have studied rates of photosynthesis in various crops, and some have found differences in photosynthetic rates. For example, Bhagsari and Harmon (2) reported differences in rates of CO2 uptake among 20 sweet potato genotypes. Crosbie et al. (5) have demonstrated that leaf photosynthesis of maize can be improved by recurrent selection, and Mahon and Hobbs (12) have reported progress in the selection of peas for high photosynthetic CO2 exchange rate.Cieply (3) concluded that assimilation rates can be used as a physiological criterion for rapid selection in potato breeding. Moll and Henniger (13) measured rates of "4CO2 uptake by 18 clones of potato under standard conditions and obtained a correlation of 0.6 (P < 0.01) between tuber yield and 'whole photosynthetic capacity' (the product of photosynthetic rate and leaf area). Col-
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