Stereological Methods for Measuring Internal Leaf Structure Variables

A recent increase in research into ecological leaf anatomy is based partly on the effects of leaf structure upon photosynthesis. Hence, it is desirable to have efficient methods for measuring various aspects of internal leaf anatomy, such as percent air space and cell wall area per unit volume of tissue. Stereological methods make use of point counts and of counts of the number of intersections of sampling lines with tissue outlines on planar sections. Their practical use for measuring plant tissues is described, with special reference to highly directional tissue like palisade mesophyll and wood. In particular, the method for estimating cell wall area per unit volume requires the choice of a numerical factor which varies with tissue type. The factor has values of 2 for unoriented tissues, pI/2 for cylinders cut in cross section, and (p/2) 2 for cylinders. in longitudinal section. An interpolating function to derive a value of the factor for tissues of intermediate type is also described. Leaves from two species of composites from contrasting habitats are compared, to demonstrate the usefulness of the methods.