1. Research& Analysis, North Europe Division, Swedish Match, SE-118 85 Stockholm, Sweden
2. Dept. of Crop Science, N.C. State Univ., P.O. Box 8604, Raleigh, NC 27695-8604, USA
3. Dept. of Biological and Agricultural Engineering, N.C. State Univ., P.O. Box 7625, Raleigh, NC 27695-7625, USA