1. J.D. Fryer, and S.A. Evans(1968 ) Weed Control Handbook, Vol. 1. Principles , Blackwell Scientific Publications, Oxford, pp.494 .
2. J.D. Fryer, and R. Makepeace(1972 ) Weed Control Handbook, Vol. 2. Recommendations , Blackwell Scientific Publications, Oxford, pp.424 .
3. F.H. Perring, and S.M. Walters(1962 ) Atlas of the British Flora . Thomas Nelson & Sons Ltd., pp.432 .