1. Dijkshoorn, W. and 't Hart, M. L., The effect of temperature upon the cationic composition in perennial ryegrass. Neth. J. Agr. Sci.5, 18 (1957).
2. Ferrari, Th. J., An agronomic research with potatoes on the river ridge soils of the Bommelerwaard. Verslag. Landbouwk. Onderzoek.58.1, 132 pp. (1952).
3. Ferrari, Th. J., Not yet published.
4. Hoagland, D. R. and Broyer, T. C., General nature of the process of salt accumulation by roots with description of experimental methods. Plant Physiol.11, 471 (1936).
5. Kemp, A. en 't Hart, M. L., Grass tetany in grazing milking cows. Neth. J. Agr. Sci.5, 4 (1957).