8 4 
Journal of Agricultural Research 
Vol. XXV, No. 2 
inoculated plants, a dying of the leaves in spots and streaks which 
frequently was preceded by slight mottling. On the progeny in the 
second generation, the mottling and uniform wrinkling was usually more 
pronounced than in the first generation. Leaf spotting and early death 
of the lower leaves also obtained in the second generation. The controls, 
in the same tuber units, remained healthy in both generations. Thus 
another case was added of great contrast between rugose mosaic and 
mild mosaic. 
In the Orono greenhouse during the winter of 1921-22, leaf-mutilation in¬ 
oculations of four Irish Cobbler hills from two tuber units were made, using 
inoculum from rugose mosaic Green Mountains. Leaf dropping appeared 
in all four hills in from 24 to 31 days, but only 7 of the 12 progeny were 
affected. Parallel inoculations of two Green Mountain hills with inocu¬ 
lum from an Irish Cobbler leaf-roll hill gave negative results in both 
generations. The results here with two varieties are like those secured in 
other experiments within either variety. 
Table XX .—Effect of variation in the number of aphids upon transmission of mosaic , 
Washington, D. C ., winter of IQ20-21 1 
Series. 
Number of aphids introduced. 
0 
I 
2 
5 
10 
IS 
25 
012 
0:2 
2:2 
2:2 
2:2 
0:3 
012 
2:2 
3:3 
1:1 
77 . 
2 12 
2 \2 
OO 
012 
0:3 
2:2 
1:1 
SC. 
0'.2 
O: I 
2 : 2 
0:2 
0:3 
012 
O: I 
O’. 2 
i: 1 
28. 
0:2 
0:2 
0:1 
Oil 
i: 1 
0:2 
2 .’2 
AO. 
O’. 2 
0:2 
0:2 
i: 1 
41. 
i: 1 
7 1 7 
2:2 
w • 0 
O’. 2 
0:2 
1 ’. 1 
0 0 
014 
42...;. 
0:4 
0:2 
01 1 
V, T 
2:2 
*tO . 
Total. 
0:28 
1:9 
5:12 
3:n 
11:12 
4:11 
11:11 
Percentage. 
O 
11 
42 
27 
92 
36 
100 
1 Progeny of aphid-treated plants given as plants mosaic and total, respectively. Each plant grown 
from one tuber. 
CONCLUSIONS REGARDING INTERVARIETAL TRANSMISSION 
The several degeneration diseases described as being diagnosed and 
transmitted within the Green Mountain variety are also present in other 
varieties according to the results of intervarietal inoculations. Trans¬ 
mission to Green Mountains from other varieties for ascertaining the 
identity of the causal virus for various symptom complexes is analogous 
to the comparison of visible pathogenes from different sources by observ¬ 
ing them on the same medium or in the same host. Such comparison 
indicates that the same virus may induce different symptom complexes 
in different varieties and that similar symptom complexes in different 
varieties may be caused by different viruses. Quanjer also points out 
the value of comparing degeneration diseases in some standard variety 
