Low‐temperature scanning electron microscopy of birch leaves after exposure to ozone

Comparison of different harvesting and preparation pathways showed that low‐temperature SEM is an adequate method to conserve the stomatal aperture for SEM. Both critical point drying and freeze drying cause considerable artefacts. Exposure to site‐relevant concentrations of ozone led to reduced width of the stomatal aperture. Moreover, unetchable droplet‐like exudates were found on the outer face of mesophyll cells of leaves where the trees had been exposed to ozone. These exudates were later followed by collapsed mesophyll cells and ended in necrotic zones before premature leaf loss. 1991 Blackwell Science Ltd