“…CHIBNALL (8) pointed out that estimation of the diurnal changes in nitrogen from percentages based on the dry weight of the leaf gives inaccurate and misleading results, and recommended that such percentages be calculated on the less variable fresh weight of the tissue. MASON and MASKELL (37) concluded that the apparent constancy of the fresh-weight basis is largely illusory and that in the absence of specific evidence of constancy, or especially when differential treatment might be expected to affect the moisture relations of the plant, this basis, like the customary dry-weight basis, is unsatisfactory. They suggest that when it can be safely assumed that the variation in the basic dry weight during the experiment is due to variation in labile carbohydrates, a logical procedure is to base analyses on the so-called residual dry weight, i.e., the total dry weight minus these carbohydrates.…”