6 4 
Journal of Agricultural Research 
Voi. XXV, No. 2 
in the same two tuber units were healthy, as were their 4 progeny grown 
in the greenhouse. Two hills had the combination of leaf roll and rugose 
mosaic. One of these lived longer than the three hills with rugose 
mosaic alone. The other was used as a source of inoculum for leaf- 
mutilation inoculation of two hills which showed leaf dropping in 32 
and 50 days, respectively, but whose 8 progeny were healthy. Inocula¬ 
tion with leaf roll alone in four hills of two tuber units gave negative 
results which persisted in the 14 progeny. The designation of rugose 
mosaic here in Irish Cobblers is based on the results of parallel inter¬ 
varietal inoculations to Green Mountains. 
Table X. — Leaf-roll inoculations of caged Irish Cobblers in IQ 20 
Inoculation. 
Progeny, 1921. 
Series. 
Method. 
Hills. 
Tuber 
units. 
Leaf 
roll. 
I 
Grafting stalks. 
6 
20 
Per cent. 
IOO 
O 
2 
None, in cages of Series 1. 
3 
A 
—y 
9 
24 
20 
2 
Leaf mutilation. 
O 
0 
A 
Aphids and full contact. 
6 
18 
22 
*r 
C 
Aphids. 
9 
6 
oy 
<T 
0 
6 
Full contact. 
j 1 - 
22 
O 
7 
None, controls to Series 3, 4, and 6. 
i 
9 
22 
O 
Inasmuch as hill selections in 1919 gave rise to leaf-roll progeny in 
1920 (when made next to leaf-roll hills) with a tendency to show more 
leaf roll and net necrosis with greater tuber weight (41, p. 71), similar 
hill selections were made in 1920. In Green Mountains, only 7 per cent 
of 183 progeny were leaf roll and 2 per cent net necrosis. In New White 
Hebrons, 28 per cent of the progeny in 1921 were leaf roll and 22 percent 
were net necrosis. The relation to tuber weight is shown in Table XI. 
There was again an increase of each disease with an increase in tuber 
weight. 
Table XI .—Correlation in New White Hebrons in IQ21, between tuber weight, net , 
necrosis, and leaf-roll infection, at the time of planting 1 
Tuber weight. 
Number 
of tubers. 
Net 
necrosis 
in tubers. 
Leaf roll 
in tubers. 
Ounces. 
Per cent. 
Per cent. 
I 
8 
O 
O 
1 to 2 
19 
5 
II 
1 to 3 
29 
10 
, T 7 
i to 4 
36 
14 
22 
I to s 
42 
14 
21 
i to 6 
47 
15 
21 
1 to 7 
52 
19 
25 
1 to 8 
54 
22 
28 
1 Leaf-roll infection in tubers was ascertained from the appearance of their plant progeny in the early 
part of the season. 
