Frank, Z.R., Division of Plant Pathology, The Volcani Center, Agricultural Research Organization, Bet Dagan, Israel

The disease indices of homogenous populations, as compiled from field data, measure field resistance. Since the disease level in a population is the product of disease severity in diseased plants and their frequency, it may be illustrated by a rectangle. This presentation facilitates analysis of the contribution, to field resistance, of tissue resistance versus escape ability. © 1973 H. Veenman en zonen b.v., Wageningen.