July 14,1923 
Degeneration Diseases of Irish Potatoes 
47 
time showed symptoms from 4 to 10 weeks before harvest as the effect 
of aphid transmission. 
Complete contact inoculation of 10 hills inside of 5 field cages in 1919 
was accompanied by transmission of mosaic in the first generation only 
in one cage where aphids accidentally gained access (40, p. 333-34)- 
A greenhouse experiment was performed in the winter of 1919-20 
with aphids excluded by insect cages and with two healthy plants growing 
in the same pots with mosaic ones. The tubers when dug remained 
attached to the rhizomes and those of the healthy plants produced 
healthy progeny. 
In field insect cages in 1920, healthy hills grown with roots, shoots, or 
both in contact with mosaic hills (Table I) displayed no symptoms and 
had healthy progeny, except when aphids were present. 
Table I .—Mild mosaic inoculations of caged Green Mountains in IQ20 (Presque 
Isle , Me.) 
Inoculation. 
Progeny, 1921. 
Series. 
Method. 
Hills. 
Tuber 
units. 
Mosaic. 
I 
Aphids, flea beetles, and full contact (of roots and 
shoots).. 
0 5 
a x 
12 
Per cent. 
83 
0 
2 
Flea beetles and full contact. 
8 
3 
Full contact (controls to Series 1, 2). 
a 6 
20 
0 
4 
Root contact. 
a 12 
47 
0 
5 
Flea beetles and shoot contact. 
b 6 
24 
0 
6 
Flea beetles. 
b6 
26 
0 
7 
Shoot contact. 
b 6 
18 
0 
a Six 4-hill tuber units each represented in Series i or 2, 3, and 4. 
b Six 3-hill tuber units each equally represented in Series 5, 6, and 7. 
During the winter of 1921 and 1922, in a greenhouse experiment at 
Washington, D. C., 15 healthy tubers were split; one half of each tuber 
was planted in an 8-inch pot not in contact with a mosaic plant, the other 
half was planted in a 10-inch pot with a tuber half taken from a mild 
mosaic potato vine. Ten of the healthy half tubers were planted in 
contact with the mosaic seed pieces but not grafted; the remaining 5 were 
planted 6 inches from the mosaic seed pieces. Nine of the mosaic seed 
pieces represented the Bliss Triumph variety, while the remaining six 
mosaic tuber halves represented the Green Mountain variety. 
The fifteen 10-inch pots were kept under aphid-proof cages from 
December 30, 1921, when the tubers were planted, until April 11, 1922, 
when they were harvested. The fifteen 8-inch' control pots with the 
single healthy half-tuber seed pieces were kept uncaged in the same 
greenhouse as the caged lots. Three examinations for aphids during 
the course of this experiment did not disclose a single aphid within the 
cages. These observations also revealed that every vine from the 15 
mosaic seed pieces showed distinct mild mosaic mottling, and that the 
vines from the 15 healthy seed pieces remained free from mosaic mottling 
until they were harvested April 11, 1922, when the majority of the plants 
showed distinct signs of maturity. The second-generation plants from 
the healthy seed pieces like the first generation also failed to show any 
signs of mosaic mottling, while under the same conditions distinct 
