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It is shown that the leaf area: leaf weight ratio decreases with increasing leaf weight. 2. The relation between the leaf area: leaf weight ratio and leaf weight is well fitted by a linear regression equation. 3. A method of estimating the mean leaf area per leaf or per plant of a field crop by means of this regression is described. The mean weight per leaf is determined by a large sampling, and the leaf area: leaf weight ratio and its regression on leaf weight are estimated on a small subsidiary sample. 4. Alternative methods of estimation from the mean leaf weight and either the unweighted or the weighted mean leaf area: leaf weight ratio are shown to give positively biased estimates of mean leaf area. 5. It is emphasized that the small sample, from which the leaf area: leaf weight ratio and its regression on leaf weight are determined, must be a strictly random selection from the whole population.
D. J. WATSON (Thu,) studied this question.