Apr. x, 1921 
Leafroll , Net-Necrosis , and Spindling-Sprout 
69 
Table X .—Relation between tuber weighty recency of leafroll infection, and net-necrosis 
at the time of planting , in sublots of lot V-148, New White Hebron variety 
Sub¬ 
lot 
No. 
Condition of plants in the 
previous season. 
Number of tubers weighing 
Per¬ 
cent¬ 
age of 
net- 
necro¬ 
sis. 
1 ounce. 
2 ounces. 
3 ounces. 
4 ounces. 
5 ounces. 
6 ounces. 
7 ounces. 
8 ounces. 
9 ounces. 
10 ounces. 
1 
Leafroll, from net-necrosis 
tubers. 
41 
9 
2 
Leafroll. 
2 
13 
4 
3 
Healthy, next to leafroll 
hills in same row. 
10 
8 
6 
40 
4 
Healthy, near leafroll hills 
in same row. 
6 
11 
10 
7 
2 
1 
2 
1 
13 
It is evident from Table X that while the tubers are smaller in the sub¬ 
lots free from net-necrosis, there is sufficient overlapping to indicate that 
recency of leafroll infection was the dominant factor in this lot. Such 
recent inoculation was followed by net-necrosis also in lots n, no, 126, 
V-134, V-138, V-139, and V-156, but not in lots V-127, V-135, V-136, 
V-142, and V-143. The tendency for the tubers to be lighter in weight 
as leafroll is more pronounced is not surprising in view of the previous 
discussion of the effects of leafroll. 
Lot V-148 also shows the importance of proximity to leafroll hills. 
The progeny of the sublot from healthy hills next to leafroll hills con¬ 
tained three times as much net-necrosis (in terms of percentage of tubers 
diseased) in correlation with four times as much leafroll as was shown by 
the progeny of the sublot from healthy hills near leafroll hills. In addi¬ 
tion, both lots were 8 meters from the nearest net-necrosis lot. 
The previous discussion has disclosed the dominance of varietal and 
recent-inoculation factors over the tuber-weight factor in regard to net- 
necrosis. The question then arises how much correlation may exist be¬ 
tween tuber weight and net-necrosis, and incidentally leafroll infection, 
among the tubers of any sublot coming from hills in uniform conditions 
of growth and showing a high percentage of net-necrosis. Such data are 
given in Table XI. Here the smallest tubers are dealt with first, and 
more tubers in the sublot are included as progressively larger sizes are 
considered. For example, the first entry represents a sublot with 70 
tubers weighing 2 ounces, 39 weighing 3 ounces and bringing the total 
considered up to 109 as given in the column headed by “2 to 3,” 12 
weighing 4 ounces, and so on. The classes of heavier tubers contain 
fewer individuals and if dealt with separately would fluctuate too much— 
from o to 100 per cent—to permit ready perception of the effect of a 
gradual increase of the average tuber weight upon the percentage of net- 
necrosis and of leaf roll. 
