discolouration greater than two-thirds of vascular tissue 5 1 corm completely clean, no vascular discolouration attribute acronym entity discolouration of up to one-third of vascular tissue 3 method_of 2 isolated points of discolouration in vascular tissue scale_of variable_of discolouration of between one-third and two-thirds of vascular tissue 4 total discolouration of vascular tissue 6 5 pt corm discolouration scale