Gollan, T., Schurr, U., & Schulze, E. D. (1992). Stomatal response to drying soil
in relation to changes in the xylem sap composition of Helianthus annuus. I. The concentration of cations, anions, amino acids
in and pH of, the sylem sap. Plant, Cell and Environment, 15(5),
551-561. doi:10.1111/j.1365-3040.1992.tb01488.x.