6o 
Journal of Agricultural Research 
Vol. XXV, No. a 
The data in Table VII indicate that infection with spindling tuber was 
obtained with tuber and vine grafts, leaf mutilation, and aphids. In 
inoculation Series i and 2 the reaction of the second-generation progeny 
is represented, which in part accounts for a higher percentage of successful 
inoculations than in the remaining series. No doubt the second-generation 
progeny in Series 5 to 7 will show a higher percentage of infection than 
the first generation, since with spindling tuber as with mosaic and leaf 
roll, initial infections contracted late in the development of the plants in 
the first generation will not produce visible macroscopic symptoms in 
the same generation. Additional evidence on infection with spindling 
tuber by aphids is disclosed in Table XVI (inoculation No. 5, 8, 13, and 
14) and by means of leaf mutilation in Table XVIII. 
UNMOTTLED CURLY DWARF 
Curly dwarf, described by Orton (32 , p. 37-40 ), seems to be in part at 
least, a combination of two or more degeneration diseases, as has been 
suggested by Murphy (29, p . 69) and by Quanjer (39, p. 127-128). It 
will be considered as such in the following section of this paper. How¬ 
ever, a symptom complex here designated as unmottled curly dwarf of 
Green Mountains, has remained too true to type for three years to be 
considered yet as a combination of diseases, although it may eventually 
be demonstrated to be such. It consists of pronounced dwarfing, spin¬ 
dliness, dark green color of the foliage early in the season, wrinkling, 
rugosity, slight ruffling, curling, some rolling, uprightness, brittleness, 
burning, somewhat premature death, and spindling, gnarled, and cracked 
tubers (PI. n, A, B, 2, 3, 5; 12, A, 1). It may be the result of leaf¬ 
rolling mosaic and the spindling-tuber disease together with the mott¬ 
ling of leaf-rolling mosaic masked by the spindling-tuber disease. 
If so, the combination known as “mottled curly dwarf” would appear 
to be the same with the addition of mild mosaic, an assumpton that is 
hard to accept in view of the fact that the tubers are not so small and 
cracked in “mottled curly dwarf” as in “unmottled curly dwarf.” 
Leaf-mutilation inoculations were made in the open field in 1920. 
Inoculum was secured from an unmottled curly-dwarf hill and intro¬ 
duced into the second and third hills of each of four 4-hill tuber units. 
The symptoms appeared first in 1921, and again in 1922 in the open field, 
and in the winter of 1921-22 in the greenhouse, always as unmottled 
curly dwarf. Intervarietal transmission with aphids will be described 
later. 
Leaf : mutilation inoculations were made in the Orono greenhouse in the 
winter of 1921-22 in six hills from three tuber units. The two progeny 
of one of the inoculated hills showed the same symptoms as the 1921 
field symptoms resulting from the 1920 inoculations, even to the gnarling 
and cracking of the seven spindling tubers. However, the percentage of 
infection was much lower than for rugose mosaic in a parallel series of 
inoculations (p. 52). 
COMPARISON OF DISTINCT DISEASES 
The several symptom complexes, presumably different diseases caused 
by distinct though somewhat similar viruses, that have been previously 
considered in this paper may be compared in Table VIII. There a 
symptom is to be considered as absent if not noted for a disease. The 
