Summary
Anatomical variations of the leaves of Bertholletia excelsa (Brazil nut) collected at different heights of the same tree are presented here. The results agree with the postulates proposed in Zalenski's Law. It was found that from the base to the canopy of the tree (as conditions gradually become more xeric) the number of stomata/mm2 increased, the mesophyll became thicker, the leaves decreased in size, and the number of vessels increased. Our results were somewhat different from what was found in Pogonophora schomburgkiana (Leite & Lieras, 1978) where the statiscally significant differences were between the basal-middle strata, whereas in Bertholletia they were between the middle and canopy strata. This was taken to reflect differences in growing conditions and not in the mechanism of phenotypic variation (allthough we do not wish to imply that there is no difference). Comparison of the results here presented with those of Medri (1977) for Hevea brasiliensis suggests that this species is phenotypically more plastic (for leaves) than Bertolletia excelsa as in general, characters varied in a wider range. It is suggested that some phenotypically highly sensitive species may, in time, be used as bio-indicators.