Determination of the density of vascular saps (ρ)
The density of the phloem sap was measured using 0.5 µl glass
capillaries (CAMAG®, Muttenz, Switzerland) allowing the distinct
determination of bulk and volume. The bulk of empty and filled
capillaries was separately measured (Analytical Balance, Sartorius
Weighing Technology GmbH, Göttingen, Germany) and subtracted to
determine the pure mass of the phloem sap. Simultaneously, the
corresponding volume inside the capillaries was calculated and the
density was converted to gram per litre (g l-1).