J. Grainger introduced a phrase to describe the biological state of a plant that influences its susceptibility to illness. The phrase is represented by the ratio of Cp/Rs, where Cp stands for the overall carbohydrate content of the entire plant, and Rs is the residual dry weight of the plant’s stem. This concept was initially developed while studying the impact of Phytophthora infestans on potatoes. It was discovered that if the ratio was less than one during a Beaumont period, the plant remained disease-free. The idea was then extended to the study of other illnesses.