Experiments were performed to elucidate the process of uneven distribution of Ca between different parts of the plant. The Ca-contents of fruits and storage tissues are usually extremely low, and as a result local disorders may occur. The primary distribution of 45Ca was found to be closely linked to the distribution of water along the xylem vessels. During the period of fast growth no or hardly any water and 45Ca entered tomato fruits, apples, potatoes or seeds of the broad bean. This phenomenon is explained by accepting the existence of a mass flow transport in the phloem. This mass flow can supply the necessary water along with most other nutrients, but does not carry any worthwhile amount of Ca. In a further series of experiments it is demonstrated that conditions conducive to predominance of the sieve tube transport result in a lowered Ca-content of tomato fruits and increased blossom-end rot. Conditions favouring an auxilliary supply of water via the woodvessels reduce the disease incidence and the K/Ca ratio of the fruits.