July 14,1923 
Degeneration Diseases of Irish Potatoes 
5i 
plants. They also fed upon mosaic and healthy plants in the same cage. 
In some cages all plants were growing in the field soil, with roots and vines 
in contact, and in others the healthy plants were potted with only the 
vines in contact with the diseased plants. Controls with no flea beetles 
present were grown. In spite of special precautions, potato aphids 
were introduced with the flea beetles into some cages. The exclusion 
of aphids is a difficulty also experienced by others {39, p. 134 ). The 
data have been presented in Table I. No current-season symptoms were 
manifested. The second generation had mosaic only in the progeny 
of the hills inoculated by aphids. 
In this experiment (Table I, Series 4) attempts were made to test the 
possibility of transmission by larvae of flea beetles. A healthy Green 
Mountain plant was caged and outside its cage a mosaic plant was grown 
partly caged, and subjected under the small cage to severe infestation by 
flea beetles. The infested part was badly damaged but no flea beetles 
emerged at any time outside the large cage, whereas introduction of 
large numbers of this species into other large cages was followed later in 
the season by the emerging of a second generation numerous enough to 
skeletonize the laves. It seemed that the flea-beetle larvae feeding upon 
the mosaic plant did not travel far enough to reach the next hill. No 
effects were evident in either generation. 
In 1919, experiments were performed with Colorado potato beetles, 
Leptinotarsa decemlineata Say., as with the flea beetles, with similar 
negative results in both the first (40, p. 329) and the second generations. 
This beetle does not move from plant to plant as much as does the flea 
beetle. Its feeding habits result in more complete destruction and less 
wounding of the tissues. Although larger, its individuals are less numerous 
in the early part of the season when the plants are small. Altogether, 
it would seem to be less liable to prove a carrier than the flea beetle. 
nEAF-ROLUNG MOSAIC 
The symptoms of “crinkle” as described by Murphy (, 29 , p. 71-74) 
seem to be applicable in part to a leaf-rolling type of mosaic “ approaching 
somewhat to the appearance of curly dwarf,” and in part to “rugose 
mosaic” as described later in this paper. The writers here use the term 
“leaf-rolling mosaic” as designating a symptom complex that so far has 
been irreducible to simpler complexes, and that consists of slight dwarfing, 
diffused mottling, wrinkling, slight ruffling, and rolling of the upper 
leaves (PI. 2, B, 2, C, 1). It is different from mild mosaic in respect to 
the distinctness of the mottling, the presence of rolling, and the effects in 
combination with the spindling-tuber disease, and is similar to it in 
infectiousness. The tuber symptoms are a general average reduction in 
size. It is distinct from leaf roll. 
Intervarietal inoculations of Green Mountains will be described later. 
Leaf-mutilation inoculations of 10 hills within the variety in the open 
field in 1922 gave no current-season symptoms, in contrast with rugose 
mosaic. Inoculations of an apparent combination of leaf-rolling mosaic 
and the spindling-tuber disease were made within the Green Mountain 
variety in 1921 in an insect cage. Potato aphids from a “curly dwarf, 
vaguely mottled” hill dispersed and were transferred to a healthy hill 
whose progeny were curly dwarf in two tuber units and spindling tuber 
in both these two and in the third tuber unit which was not curly dwarf. 
The progeny of the diseased hill which was the source of the inoculum, 
