Sieve tube exudate was obtained from Ricinus communis plants grown on nutrient solutions with varying K: Ca ratio. The K: Ca ratio of the leaves and that of the exudate both appeared to be correlated with the ratio of the nutrient solution. The observed correlations explain the generally observed linkage between the Ca-level in transpiring green plant parts and the degree of severity of Ca-deficiency disorders sometimes observed in fruits, seeds or other carbohydrate sink regions.