May 19,1923 
573 
Relation of Soil Factors to Infection of Oats 
A uniform soil moisture of 36 per cent (equivalent to 10 grams of 
water to 100 grams of dry soil with a soil saturation point of 27.8 per 
cent) was maintained throughout the experiments from which the data 
in Table III were obtained. 
TabliB III .—Effect of different soil temperatures on infection of Avena nuda by Ustilago 
avenae, when soil moisture was maintained at j 6 per cent 
Average temperature. 
t)ry seed. 
Soaked seed. 
Clean 
plants. 
Smutted 
plants. 
Clean 
plants. 
Smutted 
plants. 
C. 
Per cent. 
Per cent. 
Per cent. 
Per cent. 
8® .. 
33 
67 
20 
80 
12°... 
50 
50 
10 
90 
15® . 
0 
100 
0 
100 
18° . 
0 
100 
0 
100 
21® .'. 
0 
100 
0 
100 
23^ . 
0 
100 
25 
75 
33 
67 
8 
92 
29° .. 
25 
7 S 
89 
II 
A soil moisture of 67 per cent (equivalent to 19 grams of water to 100 
grams of dry soil) with a soil saturation point of 27.8 per cent was main¬ 
tained throughout the experiment, the results of which are shown in 
Table IV. 
A comparison of Tables III and IV shows soil temperature to be 
a limiting factor in infection. The extent of its importance, however, 
varies with the amount of water present in soil or seed. 
Tabi,E IV .—Effect of different soil temperatures on infection of Avena nuda by Usti¬ 
lago avenae when soil moisture was maintained at 6 y per cent 
Average temperature. 
Dry seed. 
Soaked seed. 
Smut-free 
plants. 
Smutted 
plants. 
Smut-free 
plants. 
Smutted 
plants. 
C. 
Per cent. 
Per cent. 
Per cent. 
Per cent. 
9 ^ ... 
100 
0 
91 
9 
12°. 
47 
S 3 
63 
37 
16°. 
13 
87 
72 
28 
21 ^^. 
17 
83 
71 
29 
26^.. 
39 
61 
67 
33 
29'’ . 
94 
6 
100 
0 
The results given in Table V are based upon the totals secured from a 
large number of series of experiments and are based on a total of 1,489 
plants. The soil moistures are indicated in the table, and the soil-satura¬ 
tion point varies from 39 to 41 per cent. Air-dry seeds were used through¬ 
out. 
The totals under 80 per cent soil moisture are not based on results 
obtained from as large a number of plants as in either of the other mois¬ 
ture tests. The high soil moisture was unfavorable for the germination 
of the grain and many series were reduced or failed utterly as a result, 
but the percentages given were based on a sufficiently large number to 
justify inclusion in the results. 
