This is an allergenic tree pollen. In nonaqueous media, transparent translucent, isotropic grains are oblate spheroids and look like prunes or footballs with one or two deep folds (Figure PA16-1). In aqueous media, the tannish grains are rounded triangles (Figure PA16-2). Three furrows taper to sharp ends at the poles. The granular skin, or exine, is about 3 µm thick and the diameter is about 35 µm. Acid fuchsin is the stain used in Figure PA16-2.
At 100X, these football grains are about 20 x 40 µm. At 1000X, several lengthwise creases or folds are apparent. A myriad of tiny pores, mostly less 1 µm across are visible at 1000X; but at 10,000X, inner structures are also visible through the exine pores.