The expulsion of viscous sap from a tissue or organ; the genesis of such a secretion may either be outward, representing a discernible sign, as seen in Pseudomonas mors-prunorum’s cherry bacterial canker and Cladosporium cucumerinum’s cucumber gummosis, or inward, culminating in the impregnation of lysigenous cavities in xylem or phloem, or the blockage of channels due to wounding or infection by vascular pathogens.