1. Cowling, D. W., and Kelly, A. F., Grass, clover and lucerne trials in O.E.E.C. countries. European Productivity Agency. Part one. Trials with grass and clover in O.E.E.C. Countries. Project No. 210 (1960) 9–152.
2. Hughes, R., The herbage production of two strains of perennial ryegrass. Bull. Welsh Pl. Breed. Sta. Ser. H. No. 18, (1956) pp. 78.
3. Jenkin, T. J., Perennial ryegrass at Aberystwyth. Welsh J. Agric. 6, (1930) 140–165.
4. Lazenby, A. and Rogers, H. H., The evaluation of selection indices for yield in grass breeding. Proc. 8th Int. Grassl. Congr. (1960) 303–307.
5. Miles, D. G., and Walters, R. J. K., Assessment of perennial ryegrass. Rep. Welsh pl. Breed. Sta. 1960 (1961) 53–55.