98 
Journal of Agricultural Research 
Vol. XXV, No. a 
Table XXV .—Effect of difference in time elapsed between leaf-mutilation inoculation 
with mild mosaic and removal of tubers 
Tuber- 
unit 
series. 
Inoculation period. 
Exposure of first flower-bud cluster 
Fifteenth day after bud exposure.. 
Thirtieth day after bud exposure.. 
3 2 
Exposure of first flower-bud cluster 
Date of 
tuber 
Progeny mosaic. 1 
removal 
(number 
of days 
after inocu¬ 
lation). 
Number 
inocu¬ 
lated. 
Mosaic. 
40 
29 
Per cent. 
55 
25 
3 2 
66 
IO 
3 i 
3 
10 
9 
33 
20 
11 
82 
30 
10 
100 
40 
11 
9 i 
1 1 hill from each tuber. 
2 Series 1,2, and 3 of Table XIX, excluding plants inoculated before anthesis. 
* Series 8 of Table XIX. 
It has been reported (40, p . 318) that a small proportion of tuber 
units may contain both healthy and mosaic hills, and that in such mixed 
tuber units the diseased hills are at first about evenly distributed between 
bud-end hills and stem-end hills but later are more common in the bud- 
end hills. The difference thus shown at first between sister hills in 
regard to mosaic is apparently due either to unequal retardation of the 
appearance of symptoms or to unequal distribution of the virus in the 
tuber. The later development of the difference between bud-end and 
stem-end hills may be due, as far as is known, to the greater number 
of eyes in the bud-end quarters and the resulting better chance to include 
a diseased eye, or to field infection that affects the faster-growing bud- 
end plants more and that produce symptoms apparent the same season. 
In some cases of possible early field infection with current-season 
symptoms, at first only part of a hill or stalk is diseased—either one branch 
or the upper leaves or even one side of a branch, and the infection then 
spreads to the new growth, whereas perpetuation by tubers from diseased 
hills is followed by uniformly distributed symptoms. This partial 
infection appears later than that which evidently follows tuber perpetua¬ 
tion, being in 1921 about the only type found after the second roguing 
in a rcrgued and isolated seed plot that contained aphids earlier in the 
season. It is correlated with the presence in the field of virus diseases 
especially of the more injurious and virulent types, being more abundant 
in the experimental plots than in commercial fields, where it is found 
infrequently. Furthermore, it is found, in experimental plots, indis¬ 
criminately in partly diseased lots, in lots from stock that came from 
healthy fields and that are healthy in commercial fields, and in lots with 
the preceding generation grown under cages or in greenhouses with no 
opportunity or evidence of infection occurring. Murphy has noted such 
partial display of current-season symptoms ( 29 , p. 62-63). 
In 1920, several thousand Green Mountain tubers from many sources, 
mostly experimental plots, were split in two and planted as 2-hill tuber 
units. Thirty-seven tuber units either were partly mosaic—that is, with 
one or more stalks partly or wholly healthy, in the first week of July 
(when progeny of all-mosaic lots planted in the same field in the same 
