Affiliation: | Istituto di Botanica, Universitàdi Messina C.P. 58, I-98166, Messina, S. Agata, Italy; Dipartimento di Biologia, Universitàdi Trieste, via L. Giorgieri 10, I-34127, Trieste, Italy; USDA Forest Service, Northeastern Experiment Station, 705 Spear Street, Burlington, VT 05402-0968, USA; To whom correspondence should be addressed. E-mail: |