This study indicated that the reduction in leaf thickness and
thickness of all histological components were not significant
affected by O3. Significant decrease by 27% and 17% occurred in
sensitive leaves compared to tolerant leaves of Fraxinus pennsylvanica
and Prunus serotina after exposure to ozone. Also, total leaf
thickness was less for sensitive trees for both species (Bennett et
al., 1992). In addition, elevated ozone led to thinner leaves of birch
(Oksanen et al., 2005). In contrast, palisade layer thickness of birch
increased after ozone exposure (Paakkonen and Holopainen, 1995).