THE MEASUREMENT OF TOLERANCE TO EDAPHIC FACTORS BY MEANS OF ROOT GROWTH

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Abstract
SUMMARY: The tolerance of plants to toxic metals is frequently measured by comparing rates of root growth in culture solutions with and without the addition of the metal, but many variants of the technique are available. Toxicity is often reduced by the presence of other ions, particularly calcium. Control growth rates may be measured beforehand on the same roots or in parallel on a duplicate set. With a single toxic concentration tolerance is defined as the ratio of the two growth rates; with a range of concentrations the slope of the regression of growth on concentration may be used, but there are some complications with stimulation at low concentrations. Probit analysis may be valuable. There is good evidence that tolerance differences are largely of genetical origin.