The Movement of Ions from the Xylem Solution into the Sieve Tubes of Willow

Abstract

Sieve-tube exudate was obtained as honeydew from colonies of the aphid, Tuberolachnus salignus (Gmelin), feeding on isolated stem segments of willow. Potassium and sodium were shown to be present in this honeydew. On perfusing the xylem with a solution of potassium or sodium chloride, a considerable uptake of the cation took place. This uptake was followed, after a period of several hours, by an increase in the concentration of the particular cation in the honeydew. A relationship was shown to exist between the concentration of these cations in a given segment and their concentration in honeydew obtained from that segment. No such relationship existed, however, with different segments. These results are discussed in relation to the factors which possibly control the movement of solutes into the sieve tube.