70 
Journal of Agricultural Research 
Vol. XXV, No. a 
ties or as to mild mosaic in Green Mountains, for reasons given in the 
footnotes. It was obvious that rugose mosaic had been transmitted to 
all three varieties from Rurals, and from two seedling varieties to two 
inoculated varieties (Series i, 2, and 3), and that streak and the streak 
combination with rugose mosaic, after transmission and tuber perpetua¬ 
tion, were much worse in their effects than rugose mosaic alone. Leaf 
roll was not transmitted. Leaf-rolling mosaic from the Rurals (Series 1) 
was combined with spindling-tuber disease, giving mottled curly dwarf. 
The conclusions from this experiment are that leaf-roll was not trans¬ 
missible under the prevailing conditions; that mild mosaic and spindling- 
tuber disease were present and uncontrolled; that leaf-rolling mosaic 
was transmitted from curly-dwarf Rurals in combination with rugose 
mosaic and possibly with spindling-tuber disease, being combined with 
the latter in Green Mountains to form mottled curly-dwarf; that rugose 
mosaic was transmitted from four dissimilar symptom complexes in 
three varieties; and that streak, both alone and with rugose mosaic, was 
transmitted and was perpetuated by the tubers, with effects in the 
second generation similar for the single and combined state and at the 
same time unlike the effects in the first generation. 
Several other interesting facts may be noteworthy. In a number of 
tuber units (Table XIV, rows i-B, i-D, and 2-J), mosaic was perpetuated 
by the seed tuber and was present when a more severely injurious disease 
was introduced to some of the hills. The inoculated hills (not described 
in Table XIV) became different from the others in these units after the 
incubation period, and the original mosaic symptoms were somewhat 
obscured. In Series 1 and 3 the Irish Cobblers showed fine or small 
spotting, but not the Green Mountains. Such spotting is common on 
Irish Cobblers which are found diseased as the result of natural field 
infection, presumably following rugose-mosaic transmission by insects. 
In Series 1 the Rurals showed streaking which was not in the other 
varieties, but they were inoculated with juice taken two days later from 
different hills in the same lot, so a different virus may have been 
present. Variation in completeness of symptom complexes in the same 
row following the introduction of the same inoculum was observed, as 
described in Table XV. Such variation may be due only to differences 
in the size of the plants at the time of inoculation, and therefore be due 
to the leaf-surface conditions of inoculation rather than to differences 
in the inherent nature of the plants. 
