Sept. 33,1918 
Pemphigus populi-transversus 
581 
They give P. monilifera as a synonym under P. deltoides (the name used 
in this article), a species which, they state, occurs from Quebec to the 
Northwest Territory, south to New Jersey, Florida, Colorado, and New 
Mexico. P. trichocarpa and P. fremontii apparently occur in the Western 
States. 
FORMATION OF GALLS 
In transferring the species from crucifers to sprouting cuttings of 
Populus deltoides it was found that the petioles of young leaves, just 
out of the bud, are apparently the only ones upon which galls begin to 
develop. A transverse groove first appears on the petiole where the 
young stem mother has located, the developing petiole gradually bend¬ 
ing at this point. The tissue surrounding the groove, which is on the 
inside surface of the bent petiole, gradually enlarges until a hollow 
globular gall, with a transverse slit on the surface opposite the petiole, 
is formed around the stem mother. Galls found in the field on May 17 
were roughly spherical in shape and varied in diameter from % to 
inch. Just before the leaves fall from the trees some of the galls reach 
a greatest diameter of nearly an inch. The galls vary considerably in 
shape, length of the transverse slit, and development of the lips (see 
PI. 83; 84, A-E). While the general color of the gall is the same as that 
of the petiole, a portion of the surface often has a reddish tinge. 
Practically all of the galls occur somewhere on the leaf petioles, though 
what seem to be the galls of this species have been found on the new stem 
growth to which the petioles are attached. The galls usually occur 
singly, but as many as three have been seen in juxtaposition on one 
petiole. 
In midsummer the gall contains, and indeed is often filled with, the 
comparatively large stem mother, her progeny in various stages of devel¬ 
opment, all covered with waxy secretion, together with molted skins 
and usually with liquid globules. 
DATES WHEN GALLS ARE FOUND AT BATON ROUGE 
In 1917, at Baton Rouge, winged viviparous females and the true 
sexes produced by them were taken in a small cavity on the trunk of a 
poplar tree as early as March 8. These winged females are identical 
with the winged migrants (sexupara) found about the roots of crucifers. 
On March 28, young stem mothers were found on leaf petioles where, to 
judge from the size of the galls, they had apparently been present for a 
few days only. 
During 1916, galls were noted on May 17 which had reached a diameter 
of % to K inch. On November 7, when a large percentage of the leaves 
of the poplar had fallen, few galls remained on the trees. 
