512 
Journal of Agricultural Research 
Vol. XXX, No. & 
toms appeared on the foliage of plants 
inoculated with unmottled curly dwarf 
in series D-l, E-l, and F-l; however, 
some tubers in this series were more or 
less spindling. The negative results 
obtained with aphid inoculations of 
Irish Cobblers and Rural New Yorkers 
with mild mosaic apparently suggest 
either varietal modification of symp¬ 
toms or differences in susceptibility to 
this disease. Similar reactions were 
described in the preceding section of 
this paper. The streak inoculation 
with aphids was not followed by symp¬ 
toms as with leaf-mutilation inoculation 
(see Table VI). 13 
Some comment may appropriately be 
made here upon the still frequently 
repeated statement that mosaic be¬ 
comes worse as the number of years 
increases since it has infected a given 
stock. The statement in question 
does not refer so much to the often 
demonstrated fact that the percentage 
of mosaic may increase in a stock until 
the latter is entirely diseased, but 
rather implies that mosaic is mild at 
first, then medium, and finally severe. 
According to this theory it is hard to 
explain the results described in this 
and the previous sections of the present 
paper, where inoculum introduced by 
means of leaf mutilation or aphids did 
not invariably produce mild mosaic as 
the first-year symptoms, but instead 
produced respectively the same symp¬ 
toms as were observed on the plants 
from which the inoculum was obtained 
(pi. 6, A and B). It seems preferable 
to maintain that there are several types 
of mosaic, each retaining its character¬ 
istic symptoms indefinitely under the 
same environmental and varietal con¬ 
ditions, while being perpetuated by the 
tubers or even when transmitted from 
one plant to another. 
In this connection it may be added 
that the mild mosaic plants from which 
the first Green Mountain series in 
Table VI and in Table VII were in¬ 
fected, were known to be of the eighth 
generation of a strain originating from 
mild mosaic hills selected in 1916. 
During that time the stage of mosaic 
had not become worse (pi. 7, A), 
although of course there was some 
variation with the seasons and some 
other progeny of the original selections 
had acquired additional diseases that 
made them appear to have curly dwarf,, 
bad mosaic, and mosaic dwarf. 
It may also be suggested that in 
applying these methods to potato de¬ 
generation problems in other regions, 
it will be found helpful to use insect 
cages with openings in the top (pi. 8, A) 
this feature facilitating the proper care 
of a large number of cages (pi. 8, B). 
INTERVARIETAL DISEASE-COMBINATION 
INOCULATIONS WITH APHIDS 
Combination inoculations with mild, 
leaf-rolling, rugose, and crinkle mosaic, 
leaf-roll, and spindle tuber, were made 
on Green Mountains, Irish Cobblers,, 
and Rural New Yorkers in insect 
cages in the field. Aphids were 
introduced into each cage from plants 
obtained from two sources and with 
respectively different diseases. The 
methods of inoculation, including the 
aphid transfers, resembled those de¬ 
scribed in the previous section of this 
paper. In each series aphid transfers; 
were made from the two sources on the 
same date with the exception of series 
G-2, G-3, and G-5, in which aphids 
from leaf-rolling mosaic plants were 
introduced to healthy plants 13, 7, and 
12 days, respectively, before the aphids 
from the other disease in the combina¬ 
tion ware transferred. 
Approximately 50 to 100 aphids were 
introduced to each of the three hills, 
in a cage when the height of the plants 
varied from 7 to 40 cm. The current- 
season results of these inoculations are 
indicated in Table VIII. 
The data presented in Table VIII 
show that combinations of rugose 
mosaic and spindle tuber became ap¬ 
parent in series D-3 and E-3; of 
crinkle mosaic and spindle tuber in 
series G-l; and of leaf-rolling mosaic 
and leaf-roll in series G-3. 
It is noteworthy that leaf-roll in the 
leaf-rolling mosaic and leaf-roll com¬ 
bination retained the characteristic 
symptoms of leaf-roll with leaf-rolling 
13 Since the submittal of this manuscript, observation on the second-generation plants disclosed typical 
second-generation streak symptoms. Aphid transmission of streak has also been reported by Atanasoff 
(p. 32, Rpt. Internat. Confer. Phytopath. Econ. Entom. Holland, 1923). 
EXPLANATORY LEGEND FOR PLATE 6 
A.—Representative leaves from 4 hills of the same Green Mountain tuber unit grown in cages of 
Table VI and infected with the leaf-mutilation method as follows: 1, cage A-3, rugose mosaic; 2, cage 
A-2, leaf-rolling mosaic; 3, cage A-l, mild mosaic; 4, cage A-4 (control to others), healthy. Photo¬ 
graphed on Sept. 6, 1923. Compare wdth Plate 6, B 
B—Representative leaves from 5 Green Mountain hills inoculated in insect cages with aphids and 
infected with rugose mosaic (1), leaf-rolling mosaic (2), crinkle mosaic (3), and mild mosaic (4), and 
healthy (5). Photographed on Sept. 6, 1923. Compare with Plate 6, A 
