Eight plant species were subjected to artificial acid rains of pH 2.5, 2.0, 1.5, 1.0 and 0.5 in order to determine the threshold for and symptoms of damage. The plants were Erechtites, Robinia, Pinus, Quercus, Carya, Liriodendron, Acer and Cornus from the Coweeta Hydrologic Laboratory near Franklin, North Carolina. Droplets of pH 2.0 produced brown necrotic spots on all species except Pinus while droplets of pH 1.0 produced necroses on leaves of all species examined. The size of necrotic spots increased with increasing acidity. Comparison of these results with the literature suggests that developing leaves are more easily damaged than are the mature leaves used in this study. The volume weighted average rainfall pH for Coweeta is 4.6 with observations ranging from 3.2 to 5.9. Results of this study suggest that a 10-fold increase in acidity from pH 3.2 to 2.2 in a single spring or summer storm could bring damage or death to mature leaves of dominant flowering plants in the Southern Appalachians.

Cement dust in the environment poses a threat to the proper functioning of plants in the vicinity of cement factories, as apparent from a field study conducted at different locations in the environs of Churk Cement Factory in Mirzapur District, U.P. Plant samples were collected at 100, 500, 1000, 1500, 2000, and 4000 m northeast of the factory, at three successive stages of plant growth. The plant samples collected at 4000 m distance were treated as control, as there was no apparent deposition of cement dust on their surface. The samples were analyzed with respect to foliar injury symptoms, chlorophyll concentration and phytomass accumulation. Only plants closest to the factory displayed symptoms of foliar injury. The results reveal that wheat plants at polluted sites contained decreased concentration of chlorophyll in their leaves and had reduced accumulation of phytomass, as compared to control. The grains obtained from affected sites showed quantitative and qualitative deterioration. Physico-chemical properties of the soils at polluted sites also underwent some undesirable changes. These effects had negative correlation with the distance from the factory.