July 14,1923 
Degeneration Diseases of Irish Potatoes 
69 
During the same season, in each of nine field insect cages (No. 1 to 
9 of Table XIII), a Green Mountain plant was grown between two plants 
that were of another variety and that apparently were diseased. Cages 
10 to 14 contained comparison inoculations from mild mosaic Green 
Mountains. In June, potato aphids were transferred from rose bushes 
(j< 5 ) to healthy potato plants (in entirely healthy tuber units and caged) 
and in July from these to the cages used in this experiment. The aphids 
were allowed to disperse freely within the cages. Sister hills in the same 
tuber units were grown under separate insect cages as controls, and were 
not inoculated. The results are given in Table XIII. It is of interest 
that inoculations 1, 2 and 5, were successful in inducing mosaic in the 
progeny, although the source of the inoculum was curly-dwarf plants. 
Furthermore, inoculations 1, 3, 4, and 6 in the insect cages (Table XIII) 
were, respectively, duplicates in a measure of the open-field inoculation 
Series 8, 9, 10, and 18 (Table XII). That is, the source of the inoculum 
in each pair of corresponding inoculations was the same stock of potatoes. 
The first of these four sources yielded inoculum that was ineffective with 
either method of inoculation, but not the others. This indicates that 
it was the nature of the inoculum rather than the method of inoculation 
that determined the success secured in the attempts at infection. The 
recording of more mosaic in the progeny of the caged hills than of the 
open-field hills is correlated with more frequent examination, made 
desirable by the limited number of caged hills and the expense of cage 
experimentation and possibly with more favorable conditions for infec¬ 
tion the preceding season. Even so, the symptoms were not very distinct 
or extensively distributed over the plants. 
Further open-field leaf-mutilation inoculations were made in 1920 with 
the inoculum taken from leaf-roll Irish Cobblers to Green Mountains in 
two hills of each of six four-hill tuber units, with negative results in both 
generations. 
INOCULATIONS PERFORMED IN 1921 
In 1921 the leaf-mutilation method was used again with inoculum 
obtained from several sources. The inoculum in each series was applied 
to two or more varieties, and with the exceptions of Series i and 7 was 
unrenewed—that is, the juice was expressed from a certain group of 
shoots at one time. The inoculated plants were in rows of 11 four-hill 
tuber units. One hill in each unit was inoculated with juice from mosaic 
Bliss Triumph plants and another with juice not alike, in regard to source, 
for two rows of any one variety. The date of inoculation was from 
July 4 to July 9, except for Series 6 and 8, for which it was July 19. Addi¬ 
tional data are given in Table XIV. The current-season symptoms 
make it evident that the inoculum used in Series 1 to 5 was very infective 
and injurious, while that used in Series 6, 7, and 10 was apparently with¬ 
out effect. In general, the effects of inoculation in Series 1, 2, and 3 
were similar, being those of rugose mosaic in the upper part of the plant, 
with the mottling fading, as often occurs, into diffused chlorosis with 
greater degree of maturity (PI. 12, C). The effects of inoculation in 
Series 5 were different, being those of streak in the upper part of the 
plant (PI. 5, A, C). Series 4 gave effects of both rugose mosaic and streak. 
The second-season symptoms in 1922 are also noted in Table XIV. No 
distinction was attempted between the progeny of inoculated and unin¬ 
oculated hills as to the spindling-tuber disease in any of the three varie- 
