56 Nebraska Agricultural Exp. Station, Research Bui. 12 
gether as susceptible, Jonathan and Winesap as moderately 
susceptible, and Oldenburg and Wealthy as resistant. A like 
number of inoculations in the heartwood of each variety were 
examined at the same time and grouped in the same way. 
Total growth above and below the inoculation was considered. 
There was a great deal of variation in the amount of growth 
made by the fungus in each variety, as shown by the data in 
table 14. In order to reduce the experimental error to a min- 
imum much larger numbers should be employed than those 
used in securing the above data. However, considering the 
probable error the results clearly indicate that some factor or 
factors in addition to anatomical differences operate to influ- 
ence immunity. 
Table 14 — Relation of active and inactive tissues to varietal 
susceptibility 
GROUP 
Average 
Growth in 
One-Year- 
Old Xylem 
Range of 
Variation 
Averag-e 
Growth 
in Heart- 
wood 
Range of 
Variation 
Mini- 
mum 
Maxi- 
mum 
Mini- 
mum 
Maxi- 
mum 
Inches 
In. 
In. 
Inches 
In. 
In. 
1. Susceptible 
28.03 
4.5 
44.0 
94.7 
84.5 
146.0 
2. Moderately sus- 
ceptible 
9.8 
2.5 
36.5 
65.2 
51.0 
92.0 
3. Resistant 
3.1 
0.5 
7.5 
11.5 
4.5 
31.5 
If no factors other than anatomical differences operate to 
influence the rate of growth, the fungus should make relatively 
as much growth in one tissue as another. Therefore, con- 
sidering the rate of growth in inactive tissues of groups 1 and 
2 as standard it would be expected, assuming 28.03 to be cor- 
rect amount of growth in active tissue for group 1, that the 
amount of growi:h in group 2 would be 19.4 inches, but instead 
it is 9.8 inches. Considering groups 2 and 3 in the same way, 
the amount of growth in active tissue in group 3 should be 
17.2 instead of 3.1 inches. 
Branches of the different varieties sterilized by steam 
under pressure and then inoculated showed practically the 
same amount of growth in all xylem tissues. There was ap- 
proximately the same difference between woods of different 
varieties as was shown in field inoculations in heartwood. 
