The Relative Contributions of Sugars from Assimilating Leaves and Stem Storage Cells to the Sieve Tube Sap in Willow Cuttings

A method is described for the measurement of the relative contributions of sugars from the assimilating leaves and stem storage cells to the sieve tube sap in leafy cuttings of Salix viminalis L. In these experiments sieve tube sap was collected as honeydew from a small colony of aphids, Tuberolachnus salignus (Gmelin). Using this method it has been shown that in cuttings maintained under continuous illumination prior to experimentation, the leaves contribute about 75 per cent of the total sugars in the sieve tube sap. With cuttings which have been stored by keeping them in darkness, the level of labile carbohydrates in the stem storage cells decreases, in comparison with those growing in light, and the percentage of sugars in the sieve tube sap supplied by the leaves rises to 90 per cent.