July 14,1923 
Degeneration Diseases of Irish Potatoes 
81 
inoculated in comparative series. The average height of the plants at 
the time of the first inoculation was about 7 cm. 
Repeated applications with mild mosaic and spindling tuber were 
more effective than single treatments. The Irish Cobbler apparently 
shows greater susceptibility to spindling tuber than to mild mosaic. 
A distinct varietal reaction to mosaic dwarf appears between Green 
Mountain and seedling 39374, being rugose mosaic or streaking and 
spotting, respectively, suggesting the combination for mosaic dwarf to be 
rugose mosaic and streak. The occurrence of spindling tuber in the con¬ 
trols in the Irish Cobbler variety resulted from field infection in 1921. 
Since in each series, hills 1, 2, and 3 in the inoculated lot are progeny 
from seed pieces of the same three tubers, respectively, as hills 1,2, and 
3 of the control lot, it is quite apparent that spindling-tuber infection 
resulted from inoculation in some units in which the controls remained 
healthy (Series A-III, all three hills; B-III, hill 3; E-III, hill 3 (PI. 9, 
B); F-III, hill 3.) 
intervarietal inoculations in the greenhouse 
Results previously reported from greenhouse experiments on inter¬ 
varietal inoculations consist of the transmission of mosaic by juice 
transfer from Green Mountains to Bliss Triumphs (45, p. 253-55), and 
of leaf roll by aphid dispersal from both Green Mountains and Irish Cob¬ 
blers to each of these varieties (41, p. 57-58). 
In the Orono greenhouse in the winter of 1920-21, mild mosaic inocu¬ 
lations of Green Mountains were made with several juice-transfer methods 
(Table XIX, Series 1 to 10). The inoculum was always obtained from 
mild mosaic Bliss Triumph hills. 
It will be noted in Table XIX that in Series 1 to 7 inoculation of any 
type was performed at four different times. The inoculated plants in 
this experiment were potted separately but consisted of 4-hill tuber units. 
The four plants grown from any one tuber were inoculated, respectively, 
at the four different times which were not absolute dates but corresponded 
to certain stages of development of the plant. The first plant to reach 
a height of 10 to 15 cm., or Stage I, was inoculated immediately. 
All four plants were observed in regard to the time when the terminal 
shoot exposed the first flower-bud cluster by opening and growing 
beyond it, and this was considered as the anthesis stage (II) since all 
potato buds abort in the Orono greenhouse at this season. The first 
plant of each tuber unit to reach the stage of anthesis, disregarding the 
one already inoculated at Stage I, was inoculated at that time, the next 
one to do so was inoculated 15 days after anthesis (at Stage III), and the 
last one was inoculated 30 days afterwards (at Stage IV). All were dug 
at Stage VIII, which was 40 days after the so-called anthesis, or II, 
25 days after III, and 10 days after IV. The date of anthesis was not the 
same for all plants of a tuber unit, differing from 1 to 13 days, the same as 
for the different tuber units. In Series 8 to 10, inoculation was performed 
at the same stage of maturity—namely, at anthesis, but the tubers were 
dug at four different times for each tuber unit. The four plants were 
harvested, respectively, 10, 20, 30, and 40 days after anthesis, which 
stages are denoted, respectively, as V, VI, VII, and VIII. The later 
the date of anthesis the shorter interval of time was allowed between 
anthesis and harvesting, to make the dates of harvesting as late and as 
close together as possible. Thfe tubers planted were dug in the field 
during the last week of July, 1920, and were planted November 15 to 19. 
