1. Adams, D. F., Mayhew, D. J., Gnagy, R. M., Rickey, E. P., Koppe, R. K., and Allen, I. W.: 1952, Ind. Eng. Chem. 44, 1356.
2. Anderson, P. J.: 1914, Plant World 17, 57.
3. Applegate, H. G. and Durrant, L. C.: 1969, Environ. Sci. Tech. 3, 754.
4. Barrett, T. W. and Benedict, H. M.: 1970, Report No. 1., TR-7 Agric. Committee, APCA, Pittsburgh, Pennsylvania.
5. Benedict, H. M. and Breen, W. H.: 1955, Proc. Third National Air Poll. Symp., Pasadena, Calif.