Jordanov, S., and A. Gudeski. “Density, Dimensions and Depth of Stomata in the Needles of Pinus Nigra in Polluted and in Clean Environment”. Macedonian Journal of Ecology and Environment, vol. 8, no. 1-2, Dec. 2003, pp. 47-54, http://mjee.org.mk/index.php/mjee/article/view/64.