ARCO SELLS TWO AGRICULTURAL RESEARCH OPERATIONS Atlantic Richfield Co said it sold its Plan Cell Research Institute unit and its Arco Seed Co operations in two transactions for undisclosed prices. The company said it sold Dublin, Calif.-based Plant Cell Research to Montedision SpA of Milan, Italy, and ARCO Seed Co to U.F. Genetics of Hollister, Calif. Atlantic Richfield said the divestitures are in line with its policy of focusing resources on oil, gas, chemical and coal operations.