1. Department of Plant Anatomy, Institute of Biology, Eötvös Loránd University, Pázmány Péter sétány 1/c, Budapest 1117, Hungary
2. Nefag Rt. Nagykunsági Forestry and Wood Industry Rt., Szolnok, Hungary
3. Centre for Agricultural Research, Institute for Soil Sciences and Agricultural Chemistry, Herman Ottó ót 15, H-1022 Budapest, Hungary
4. US Forest Service, Pacific Northwest Research Station, 3200 Jefferson Way, Corvallis, Oregon 97331