* Bowen, H. J. M., A standard biological material for elementary analysis. In P. W. Sallis (ed.), Proc. of the SAC Conference, Nottingham, UK, pp. 25–31. Cambridge: W. Heffer and Sons, 1965.
* Bowen, H. J. M., Kale as a reference material. In W. R. Wolf (ed.), Biological Reference Materials: Availability, uses and need for validation of nutrient measurement, pp. 3–17. John Wiley & Sons, 1984.
* Stoeppler, M., Wolf, W. R. and Jenks, P. J. (eds.), Reference Materials for Chemical Analysis: Certification, Availability and Proper Usage. Weinheim: Wiley-VCH, 2001. . (See pages 4, 26, 59 & 216.)