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2. IBP Handbook No. 11;E. Bennett,1970
3. Cochran, W. G. 1963. Sampling Techniques. 2nd edit. John Wiley, New York.
4. Gevers, H. O. 1976. Unpublished Ph.D. dissertation. Univ. Natal, Pietermaritzburg, Natal, Republic of South Africa.
5. Marshall, D. R., and H. D. Brown. 1975. Optimum sampling strategies in genetic conservation.In Plant Genetic Resources for Today and Tomorrow. O. H. Frankel and J. G. Hawkes, eds. IBP Vol. 2, pp. 53–80. Cambridge Univ. Press.