The significance of essential and non-essential trace elements in plants in relation to biogeochemical prospecting.
The observation that essential trace elements gave hyperbolic effects when relative accumulations (amount in plant/amount in soil) were plotted as a function of the soil content provided a more satisfactory basis for indicating essentially than investigations as to whether elements were normally or log-normally distributed in plants by a comparison of geometric and arithmetic means with the median. Another criterion of essentiality was the visual examination of histograms of element concentrations in plant material: non-essential elements tended to have a wider spread of values than essential elements. Since the range of values in the soil must also be considered, one of the best criteria of essentiality is the ratio of the coefficients of variation for plant and soil data; high plant/soil ratios indicated non-essentiality and suitability for biogeochemical prospecting. In general, plants with a specific requirement for a particular element were unsuitable for this type of prospecting unless soil concentrations ranged well above the physiological requirement of the plant for the element.