Students in a general botany laboratory course sampled leaves from the north vs. the south sides of exposed trees of four species on the campus of Southeastern Oklahoma State University. They made estimates of (1) leaf shape, (2) leaf area, and (3) specific leaf weight (SLW). The leaf shapes, areas, and SLW usually differed among species and individuals. In the early fall semester of 2001, leaves on the north and south sides of some trees differed significantly in shape, area, and SLW, but these differences did not occur in the late spring semester of 2001. This occurred primarily because the leaves of silver maple and sweet gum were larger on the north than on the south side, presumably due to lower water stress, in the fall semester; this was not true, however, of post oak and white ash. Most of the students, in written reports, correctly understood the relationship of smaller, denser leaves as both a result of and an adaptation to the greater heat load found on the south side of a tree. For most of them, it was a new experience to realize how much variation in leaf characteristics could be found in a single tree, and that this variation often follows an environmental pattern.

Key words: Aspect, plasticity, trees