TRANSPORT PATHWAYS IN SPROUTING TUBERS OF POTATO

The transport of potassium, calcium, water, and carbohydrates from a potato tuber to a developing sprout has been followed over an 8-week period. From the resulting balance-sheet calculations have been made of the concentration of ions in the xylem and phloem saps entering the sprout. Similarly, the concentration of carbohydrates in the phloem has been calculated. Predicted ionic concentrations in the xylem have been confirmed from analyses of xylem exudate. The pattern of results thus obtained indicates the presence of a circulatory system necessitating bidirectional transport within the phloem. The results obtained are therefore inconsistent with the hypothesis that a mass flow of solutes is the mechanism of translocation within the phloem. © 1969 Oxford University Press.