Mar. 15,1925 
Degeneration Diseases of Potatoes 
505 
tains and Bliss Triumphs, nothing in 
Irish Cobblers, and extreme dwarfing 
in the seedling. In both the mosaic 
dwarf and streak inoculation, therefore, 
the seedling appeared more susceptible 
to streak than the other varieties. 
In 1922 in the control cage of the B 
series, and also in that of the F series, 
there was a healthy hill whose 1923 
progeny developed spindle tuber. Each 
of these hills was grown in contact with 
a spindle tuber hill with aphids absent. 
Although other evidence on trans- 
missibility by contact, as described 
later, is negative in the absence of 
insects, it should be borne in mind that 
even grafting, aphid, and leaf-mutila¬ 
tion inoculations often give negative 
results. It will also be pointed out 
later that such diseases can spread with 
neither aphids nor contact serving as 
the apparent means. This behavior 
of control hills emphasizes the need of 
careful selection of seed tubers for cage 
experiments and the need of repetition 
and duplication of inoculation experi¬ 
ments. The latter need is also brought 
out by the facts that streak was not 
contracted in the mosaic dwarf and 
streak inoculations by Green Moun¬ 
tains, although spindle tuber was con¬ 
tracted by the same plants from the 
same inoculum, that streak was con¬ 
tracted by the seedling from the same 
inoculum, and that under other condi¬ 
tions Green Mountains have contracted 
streak readily from the same type of 
inoculation. In brief, while streak in 
one certain inoculum did not infect 
Green Mountains, it did not follow that 
Green Mountains were resistant to 
streak in other inoculations, which 
indicates that with such diseases one 
inoculation is not conclusive, especially 
if the results are negative. 
In series A-III, E-III, and E-I, a 
study of the data under “ Progeny, 
1923,” shows that the infected plants 
contracted either spindle tuber or both 
spindle tuber and mild mosaic with no 
explanation needed for the isolation and 
greater amount of spindle tuber other 
than the apparent greater infectious¬ 
ness of spindle tuber. However, in 
series E-II, of the same variety as the 
preceding series, there was still further 
separation of the viruses, some plants 
contracting rugose mosaic, some spindle 
tuber, and some both. The writers 
have no explanation to offer for this 
phenomenon, in which with all condi¬ 
tions apparently similar, a given inocu¬ 
lum affects inoculated plants in two or 
three different ways regarding the 
transmission of two diseases in the 
inoculum. Perplexity is increased by 
the fact, noted above, that streak in this 
inoculum did not affect any plants of 
these Green Mountain series. 
INTERVARIETAL INOCULATIONS WITH 
APHIDS 
Inoculations of Green Mountains and 
Irish Cobblers with rugose mosaic, leaf- 
roll, and spindle tuber were conducted 
with aphids in 1922. Instead of dis¬ 
persing from diseased to healthy plants 
in the same cage as in 1921, 10 the 
aphids were transferred from diseased 
to healthy plants grown in separate 
cages. Approximately 50 to 200 
aphids per cage were introduced when 
the plants had reached a height of 15 
to 20 cm. After feeding from 12 to 20 
days the aphids were killed with nico¬ 
tine sulphate spray. The results of 
these inoculations for 1922, as well as 
for the progeny in 1923, are given in 
Table IV. 
From the data presented in Table 
IV it is seen that inoculation was not 
followed by symptoms in 1922 or in 
1923 with the exception of series J, 
which contracted leaf-roll. Spindle 
tuber and mosaic in one hill of series 
D-I, D-II, and D-III, apparently were 
introduced in the open field in 1921, 
since the uninoculated controls in the 
same tuber unit show the same symp¬ 
toms. In series T-II spindle tuber in¬ 
fection may have resulted from aphids 
entering the cage through a hole found 
in the cage late in the season. The 
generally negative results in this ex^ 
periment disclose that under certain 
conditions aphids do not transmit these 
diseases. As noted later in Tables 
VII and VIII, aphids in 1923 caused 
infection when transferred in condi¬ 
tions apparently like those of the in¬ 
oculation series in Table IV. Whether 
these interesting variations are caused 
by differences in temperature, light, or 
other factors remains to be determined 
by further studies on the nature of 
these diseases and their transmission. 
CURRENT-SEASON SYMPTOMS FROM 
INOCULATIONS IN 1923 
INTERVARIETAL LEAF MUTILATION IN¬ 
OCULATIONS IN THE OPEN FIELD 
Leaf mutilation inoculations with 
different types of mosaic and with 
streak were made on plants of the 
Green Mountain variety in the open 
field in 1923. The effect of taking the 
inoculum from different parts of the 
10 Schultz, E. S., and Folsom, D. Op. cit. See Table XVI 
