Aspectos da anatomia ecológica de folhas de Hevea brasiliensis Müell. Arg. (The comparative anatomy and morphology of the leaf of Hevea brasiliensis at diferent microclimates and habitats were studied. Leaves of diferent strata were compared, and comparisons were made with leaves of equivalent strata between plants growing in várzea and terra firme. The results show progressive xeromorphy with increase in height (as conditions become progressively more xeric) and more scleromorphy in leaves of comparable strata of terra firme than in várzea. The results thus agree with Zalenski's law and Lleras interpretation of the same. The data here presented for Hevea brasiliensis suggest that this species shows more phenotypic plasticity than other species studied by the same authors. It is here suggested that based on comparisons of phenotypic plasticity within individuals of natural or clonal populations, it is possible, using the criteria here developed, to select genotypes that will show higher drought tolerance.