May, 1922] RAINES — VEGETATIVE VIGOR OF THE HOST 229 
Table ii 
Experiment 
I 
II 
III 
IV 
V 
Group 
Group 
Group 
Group 
Group 
a 
c 
a 
c 
a 
d 
A 
A 
No. of pustules i mm. long 
94 
20 
72 
14 
82 
22 
96 
12 
70 
8 
" " " I mm. " 
6 
20 
28 
34 
18 
30 
4 
30 
25 
24 
" " " It mm. " 
34 
38 
30 
46 
3 
24 
" " " 2 mm. " 
24 
8 
12 
8 
2 
34 
" " " 2} mm. " 
2 
4 
4 
4 
7 
" " " 3 mm- " 
2 
2 
3 
Sum of lengths of 100 pustules in mm. 
53 
134 
'■' 
130 
59 
126 
52 
131 
68 
169 
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, 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 ^ to 7^ received progressively diminishing doses of uredospores. This 
would make the amount of infection observed on the plants of the difTerent 
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 
