May, 1922] RAINES VEGETATIVE VIGOR OF THE HOST 



TABLE n 



229 



Figures 4 and 5 of Plate XII illustrate the relative size of the pustules 

 on leaves of semi-starved and of vigorously growing plants. 



Pustules attained a larger size on the more rapidly growing host plants, 

 indicating that a more luxuriant host tissue means a more luxuriant parasitic 

 mycelium. 



DISCUSSION 

 Relation between Host Vigor and Incidence of Infection 



On their face the figures obtained in the soil-culture experiments indicate 

 that in experiments I, II, III, and IV there occurred a decreased incidence 

 of infection with depression in growth vigor of the host; but in experiment V 

 the figures indicate quite as definitely precisely the opposite relation 

 namely, increased incidence of infection with depression in the growth 

 rate of the host. 



The dosage for all six groups of variables in soil-culture experiments 

 IV and V was probably essentially the same. The plants were arranged in 

 order of alphabetical designation of the groups: A, B, C, D, E, F. The 

 possibility might be suggested that in experiment IV inoculation proceeded 

 from the direction of F and that the plants from F to A were subjected to 

 progressively diminishing doses of inoculum; and, conversely, that in 

 experiment V inoculation was from the direction of A and that the plants 

 from A to F received progressively diminishing doses of uredospores. This 

 would. make the amount of infection observed on the plants of the different 

 groups a function of their positions relative to each other. But actually 

 the amount of infection observed is correlated not with the position of the 

 group but with its relative growth vigor as indicated by the mean dry 

 weight of the plants. Thus, in both experiments IV and V, group E exhibits 

 an amount of infection not like group F, next to which it was placed, but 

 like group B which it resembles in vigor of growth. We may conclude that 



