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A b s t r a c t. For a herbaceous species, the inverse of the fresh leaf surface density, the Hughes constant, is nearly conserved. We apply the Hughes constant to develop an absolute method of leafarea measurement that requires no regression fits, prior calibrations or oven-drying. The Hughes constant was determined in situ using a known geometry and weights of a sub-set obtained from the fresh leaves whose areas are desired. Subsequently, the leaf-areas (at any desired stratification level), were derived by utilizing the Hughes constant and the masses of the fresh leaves. The proof of concept was established for leaf-discs of the plants Mandevilla splendens and Spathiphyllum wallisii. The conservativeness of the Hughes constant over individual leaf-zones and different leaftypes from the leaves of each species was quantitatively validated. Using the globally averaged Hughes constant for each species, the leaf-area of these and additional co-species plants, were obtained. The leaf-area-measurement-by-mass was cross-checked with standard digital image analysis. There were no statistically significant differences between the leaf-area-measurement-by-mass and the digital image analysis measured leaf-areas and the linear correlation between the two methods was very good. Leaf-areameasurement-by-mass was found to be rapid and simple with accuracies comparable to the digital image analysis method. The greatly reduced cost of leaf-area-measurement-by-mass could be beneficial for small agri-businesses in developing countries.K e y w o r d s: leaf area, leaf mass, planimetry

Aldama dentata Llave & Lex. is a plant native to Latin America that exhibits metallicolous populations. Its ecophysiological (EP) response to Cu stress, administered as graded soil concentrations (C s ) of the fungicide copper(II) oxychloride, is examined in depth. Using a systems biology-and population dynamics-inspired approach, an r/K-driven model is proposed that satisfactorily explains the plant Cu concentration (C p ) versus C s EP response curves for the root, shoot, and whole plant. A. dentata was found to be a Cu excluder (ME). The dual role of Cu as a nutrient and toxin at low and high concentrations, respectively, manifested as a parabolic variation of the foliar area where the toxicity appeared as a second-order effect. The power-law variance of biomass (B p ) with C p expected from the universal allometric scaling law of biology was loosely followed and is discussed in terms of the mode of Cu uptake by the plant and Cu's dual physiological role. Biometric growth indices reflected the impact of Cu on the photosynthetic energy harvest. The general applicability of the r/K-driven model was corroborated by its successful application to the published C p -C s data of the well-known Cu ME, Silene vulgaris. The r-K factors suggest a new quantitative manner of comparing the phytoavailability of the metal and the plant's accumulation capability across soil types. A. dentata with high root C p but low B p diminution could potentially find use as a Cu phytostabilizer.

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