Tissue density, ρ, Young's modulus, E, breaking stress, σ, density-specific stiffness (E/ρ), and density-specific strength (σ/ρ) were determined for specimens of parenchyma, collenchyma, primary tracheids, sclerenchyma, and wood. E and σ were positively correlated with ρ for parenchyma and wood. Although no correlation between E or σ and ρ was seen for the other tissue-types, E and σ were correlated for each tissue-type (an inverse proportionality was observed for parenchyma in contrast to the other four tissue-types). Comparisons among the five tissue-types showed that E and σ are inversely proportional to ρ. Parenchyma tissue samples had the lowest E and σ and the highest ρ; wood sample had the highest E and σ and the lowest ρ. Comparisons among tissue-types indicated that σ scales roughly to the square root of E (i.e., σ = 0·69 1·51, r2 = 0·98; units in MN m-2). Also, σ/ρ = 0·03 (E/ρ)0·52 (r2 = 0·99). The interspecific scalling of plant height h with respect to stem diameter d (data taken from Niklas, 1993) was evaluated in terms of E /ρ and σ/ρ by assuming that certain tissue-types characterized the anatomy of the vertical stems of different plant groups (e.g., parenchyma for moss setae, primary tracheids for herbaceous dicotyledon stems, and wood for gymnosperm and dicotyledon tree trunks). The mean E /ρ or σ/ρ for each tissue-type was used to estimate h based mean d for each plant group. Regression of predicted h vs. d gave h ∝ d1·01. Regression of observed average h vs. observed average d showed that h ∝ d1·00. Based on the similarity of the scaling exponents, it is argued that the interspecific scaling of plant height reflects interspecific differences in the anatomy and density-specific mechanical properties of the principle tissue used to provide mechanical support to vertical stems.Copyright 1993, 1999 Academic Press