Hypothesized differential genotypic galling susceptibility of Tetradymia stenolepis Greene 1885 was not confirmed by tests of correlations between sample size and sample variance in plant-mean densities of Scrobipalpa n. sp. leaf galls and Gnorimoschema tetradymiella Busck 1903 stem galls. An alternate conceptual model, the stress-heterogeneity hypothesis, received support. The greater the stress experienced by a plant subpopulation, the more discontinuous was the frequency distribution of its plant-mean gall abundance. Also according to the model, gall formation increased with stress until a physiological threshold was exceeded, after which it dropped precipitously. Covariance analysis enabled comparisons among plots. Encounter frequency and resource density were also implicated in predicting plant-mean and branch-mean gall densities.