228 
AMERICAN JOURNAL OF BOTANY 
[Vol. 9 
in water solution at the rate of loo pounds to the acre. On August 9 the 
plants were placed out of doors to be inoculated. The experiment was con- 
cluded on August 27. Figures i and 2, Plate XI, illustrate the growth 
differences obtained between the plants of the different groups in these 
experiments. 
In table 9, the groups are arranged in order of the vigor of growth ex- 
hibited by the plants. 
Table 9 
Mean 
Mean No. of 
Mean No. of 
No. of 
Soil 
Dry Weight 
Pustules 
Pustules 
Group 
Variables 
Treatment 
of Top 
of Plant 
in Mg. 
per Ave. Unit 
Area of Total 
Leaf Surface 
per Ave. Unit 
Area of most Severely 
Infected Leaf 
A 
100 
sand 
120 
.6 
2.0 
E 
100 
acid 
.8 
27 
phosphate 
1 sand 
B 
100 
200 
•7 
2.3 
D 
100 
KCl 
202 
I.O 
3-2 
C 
100 
h sand 
.9 
3-1 
F 
100 
NaNOa 
1.2 
4-5 
Experiment V 
This was a duplicate of Experiment IV, started a week later. The seed 
was sown July 17, the plants were placed out of doors to be inoculated 
August 10, and the experiment was concluded August 31. The results are 
shown in table 10. 
Table 10 
Mean 
Mean No. of 
Mean No. of 
No. of 
Soil 
Dry Weight 
Pustules 
Pustules 
Group 
Variables 
Treatment 
of Top 
of Plant 
in Mg. 
per Ave. Unit 
Area of Total 
Leaf Surface 
per Ave. Unit 
Area of most Severely 
Infected Leaf 
A 
100 
sand 
47 
5-1 
II. 6 
B 
100 
i sand 
acid 
53 
5-1 
1 1. 8 
E 
100 
93 
5-2 
II-3 
phosphate 
C 
100 
+ sand 
93 
4-5 
9-5 
D 
100 
"KCl 
96 
4.4 
10.2 
F 
100 
NaNOs 
359 
3-1 
7.6 
Relation between Host Vigor and Pustule Size 
In all five of the soil-culture experiments there was evident a marked 
decrease in the size of the rust pustules on the host plants the growth rate 
of which was depressed. The lengths of 100 contiguous pustules on plants 
from groups a and c of experiment I; groups a and c of experiment II; 
groups a and d of experiment III; groups A and F of experiment IV ; and 
groups A and F of experiment V were found to fall into the classes 
shown in table 11. 
