“…Changes of permeability have repeatedly been supposed to be involved with the periodicity of exudation (GROSSENBACHER 1938;SKOOG, BROYER and GROSSENBACHER 1938;ENGEL and FRIEDRICHSEN 1952), but it seems that no investigation has ever been made to find out whether the permeability does actually change. SKOOG, BROYER and GROSSENBACHER found that the amounts of salt present in the sap of Helianthus annuus also fluctuated, while the periodicity could be intensified by applying indole acetic acid to the stem.…”