580 
Journal of Agricultural Research 
Vol. XIV, No, 13 
• 
Pemphigus, the infestation being similar to that which occurs on cru¬ 
ciferous roots under field conditions. It was evident, when the growth 
of the plants in this box was compared with that made by plants of the 
same age in an uninfested box, that they had been affected by the pres¬ 
ence of the aphids at their roots (PI. 84, F). In fact, the turnips died 
before winged migrants appeared, though probably not altogether be¬ 
cause of the insect infestation. 
Winged migrants from galls were also placed on turnips growing in 
pots in the greenhouse. The soil in these pots had been heated previ¬ 
ously to a temperature sufficient to kill insect life, and the pots were 
covered with cloth-covered wire frames. Later, examination showed 
wingless individuals of Pemphigus sp. to be present on the roots, but 
again the plants died before the winged forms appeared. Before the 
plants died, however, a number of the wingless aphids were transferred 
to pots covered with cloth containing cabbage plants, the roots of which 
had been dipped in a mixture of water and nicotine sulphate before they 
were planted. On March 2 of the following year winged viviparous 
females, such as are found in the colonies at the roots of crucifers, were 
observed. No aphids appeared on the roots of control plants. 
These experiments, together with others that have been carried on, 
indicate that the forms found on poplar and on crucifers belong to the 
same species. Additional proof is furnished by the fact that from poplar 
trees in the spring were taken winged viviparous females which agree with 
winged migrants found at cruciferous roots at that time of the year, 
and that during late summer and during the fall there were collected from 
the leaves of crucifers winged viviparous females which are identical 
with those found in galls of P . populir-transversus. 
DISTRIBUTION AND HOSTS 
The species has been recorded as occurring on poplar in California (16, 
P . 37 2 i *9y P . 39$; zo, p . 699), Texas (j, p. 15-16), Colorado (1; 7, p. 116; 
22 , p . 98), Kansas (12 , p . 22 , 23), Nebraska (18, p. 12 ), Missouri (j, 
p . 15-16) , Iowa (5, />. 130), Minnesota (2 , p, 20 , 21), Illinois (77, p . 411), 
Indiana (21 , p . 208 ), New York ( 9 , p . 561-562; 15 , p. 247, 620 , 655-656; 
15, P * 355 ) > and Massachusetts (15, p . 355). Mr. Parker has collected it 
at Lovell, Wyoming, Dr. Gillette has specimens from Arizona, and 
Mr. Davis writes that he has records of its occurrence in Wisconsin, 
Michigan, and Ohio. Mr. H. F. Wilson has taken it in Wisconsin, and 
the writer has seen galls, apparently made by this species, at Agricul¬ 
tural College, Miss., and Jacksonville, Fla. 
Four species of the genus Populus, balsamifera , monilifera , trichocarpa, 
and fremontiiy have been mentioned as hosts. Britton and Brown (8, 
p . 491 , fig. 1165; p. 493, fig . 1172) give the following distribution for 
P. balsamifera: 
Newfoundland to Hudson Bay and Alaska, south to Maine, New York, Michigan, 
Idaho, and British Columbia. 
