Abstract
Air pollution caused by the combustion of coal at the Badarpur Thermal Power Plants, New Delhi, had a bearing on size and amount of wood elements across the tree trunk of Indian blackberry (Syzygium cumini Skeel.). Compared with the control, vessel elements in different positions along pith to cambium were significantly shorter (31-49%) and narrower (23-37%) in trees growing at the polluted sites. Moreover, vessel frequency (number of vessels per mm(2)) and consequently the vessel area on transverse surface of the wood were lower than in the control in each part of the wood sample examined. The difference at different positions along the wood-core radius in the control and stressed trees varied was 4-58% for vessel frequency and 17-32% for vessel area. Xylem fibres also showed, like vessel elements, a significant decrease in length as well as diameter at each of the positions analyzed. Vulnerability factor of the wood increased with tree age as well as air pollution, thus showing that the trees were consistently vulnerable to conditions of water stress created by the environmental degradation. The capability of trees to retain their mesomorphic character was enhanced with age but somewhat retarded under the pollution stress.