July 14, 1923 
Degeneration Diseases of Irish Potatoes 
79 
As indicated in Table XVII, the current-season reactions of the varie¬ 
ties inoculated with juice from vines showing different types of mosaic, 
dwarf, and streak symptoms, were rugose mosaic and streak or combi¬ 
nations of these. Streak alone resulted from inoculations with juice 
from a Green Mountain lot inoculated in 1921 with juice from a streak 
plant in a seedling variety (Series 14, 15, and 16). Streak, therefore, 
has appeared without apparent combinations in three succeeding gener¬ 
ations, including two in Green Mountains and Irish Cobblers as the result 
of leaf-mutilation inoculation. As indicated, the second generation 
plhnts used as source of inoculation for streak in 1922, were badly 
dwarfed and died early—before tuber formation. Similar phenomena 
were obtained with the progeny of plants inoculated in 1921, with juice 
from a mosaic dwarf plant adjacent to the streak plant, of the seedling 
variety, mentioned above (Series 10, 11, and 12). Here some of the 
inoculated hills produced stalks showing streak alone and rugose mosaic 
alone, as well as a combination of these symptoms, suggesting that 
mosaic-dwarf in the original seedling plant may have been a combination 
of rugose mosaic and streak, the severe dwarfing being due mainly to 
streak in the combination. These two inoculations are different from 
the others in that they produced streak alone in Green Mountains and 
Irish Cobblers while the others produced rugose mosaic in close associa¬ 
tion with any streaking seen in these varieties. They are also different 
because the source of inoculum was extremely dwarfed plants quite 
unlike the plants, with rugose mosaic or other symptom complexes, that 
served as sources of inoculum for the other inoculations. 
It seems probable that streaking may be a prominent first-season 
symptom of two diseases—streak and rugose mosaic—and not always a 
sign of streak. This view of the uncertain value of the one symptom of 
streaking as a sign of the symptom complex or disease of streak is 
pointed out by Orton (33, p. 100 ), and is supported by the writers’ 
comparison of first-season and second-season symptoms in a number of 
lots with rugose mosaic the second season. Streaking was more common 
as an apparent first-season symptom of rugose mosaic in Bliss Triumphs 
and Rurals (Table XVII, Series 81, 85, 89, and 107). Whether other 
diseases in several combinations used here (Series 18 to 20, 79 to 81, 83 
to 85, and perhaps others) were transmitted along with rugose mosaic 
and merely did not show current-season symptoms, can be learned only 
from the second generation in 1923. The consistent emergence, from 
combinations, of rugose mosaic in 1922, indicates that the other diseases, 
whether also transmitted or not, were of a less virulent type. Modifica¬ 
tion of rugose mosaic symptoms in combination with other diseases 
occurred in Series 10 to 12, 18 to 20, 79 to 81, and 127 to 128. The same 
thing, or else varietal modification of rugose mosaic symptoms, was shown 
in Series 105 to 107, 123 to 124, 130 to 131, 133, hi, and 119. 
In addition to those in the open field, other leaf-mutilation inoculations 
were made in insect cages located in the same field. As indicated in 
Table XVIII, repeated inoculations with mild mosaic and spindling- 
tuber were made in Series A-III and B-III, while but a single application 
was made in the remaining series, which included juice from mosaic 
dwarf and streak as well as from mild mosaic and spindling-tuber plants. 
Plants for the source of mild mosaic and spindling-tuber inoculum were 
grown in cages since 1920, inclusive, and for mosaic dwarf and streak 
since 1921. As indicated, three different varieties and one seedling were 
