[Reprinted from the AMERICAN JOURNAL OF BOTANY 9: 183-203, April, 1922.] 



VEGETATIVE VIGOR OF THE HOST AS A FACTOR INFLU- 

 ENCING SUSCEPTIBILITY AND RESISTANCE TO 

 CERTAIN RUST DISEASES OF THE HIGHER 

 PLANTS' 



i 



M. A. RAINES 

 (Received for publication July 13, 1921) 



INTRODUCTION 



Studies on the cereal rusts were made covering various phases of the 

 phenomena of rust epidemiology, including the effects of season, age of the 

 host plant, etc., on its susceptibility and on the virulence of the disease; 

 effects of varying dosage in securing inoculation; effects of the general 

 nutritional condition of the host, etc. In carrying out these studies I have 

 had the opportunity to convince myself of the frequently observed fact that 

 health and vigor of the host favor rather than hinder its inoculation by a 

 rust and the further development of the diseased condition. This observa- 

 tion has frequently been made and more or less casually reported in the 

 literature on the rusts and other fungous diseases of plants. The significance 

 of such observations in relation to general theories of immunity and resis- 

 tance to disease has, however, nowhere been adequately recognized, and 

 I have thought it worth while to bring together the available evidence 

 bearing on this point. 



It is a commonplace of pathological theory that the health and vigor of 

 an organism and its susceptibility to disease are antithetic variables, that 

 as one increases or is increased the other diminishes or is diminished corre- 

 spondingly. Adami (1910, A i: 409), summarizing the subject of predis- 

 position to disease, lists the causes of acquired susceptibility as (i) social 

 and environmental conditions; (2) injury; (3) malnutrition; (4) previous 

 attack of the same disease or other infectious disease; and (5) exhaustion; 

 all of them factors diminishing the vitality of the host. Zinnser (1914, 

 p. 59), discussing the broader principles of infection and resistance, states: 



A person suffering from functional impairment of any kind is more likely to permit the 

 invasion of a pathogenic microorganism than is a perfectly healthy well-nourished indi- 

 vidual of the same species. 



Kolmer (1917, p. 101) says, similarly: 



Acquired susceptibility . . . may be due to various factors, most of which lead to a 

 state of reduced vitality, normal physiologic processes being impaired to a greater or less 

 degree. 



1 The list of literature cited will be found at the conclusion of the second paper of 

 this series. 



