1. F. Bangerth, D.R. Dilley and D.H. Dewey, J. Am. Soc. hort. Sci.97, 679 (1972).
2. P.O. Tingwa and R.E. Young, J. Am. Soc. hort. Sci.99, 540 (1974).
3. R.B.H. Wills, S.I.H. Tirmazi and K.J. Scott, Hort. Sci.12, 551 (1977).
4. R. Amesquita-Garcia, Ph.D. thesis, Mich. State University (1972).
5. E.C. Lougheed, E.W. Franklin, S.R. Miller and J.T.A. Proctor, Can. J. Pl. Sci.53, 317 (1973).