DEVELOPMENT OF PHYLLOXERA VASTATRIX LEAF GALL 34 1 
Riley (24) and by Cornu (8). Successive daily measurements of the 
growth of galls shows that 12 to 15 days are necessary for complete 
development. 
V. Histological Development of the Gall 
During the winter of 191 3, cuttings from a Vitis vulpina vine were 
grown in the greenhouse, and in the following spring, when the first 
galls appeared out of doors, some of the nymphs were taken out of a 
gall and placed on young leaves of cuttings growing in the greenhouse. 
Twenty-four to forty-eight hours later, the first signs of gall formation 
appeared. The nymph, which had been placed on a bud leaf, as the 
bud was opening, had located itself on a primary vein, and as the 
young leaf grew free from the bud scales and opened so that its whole 
upper surface became visible, the insect was seen in a shallow depres- 
sion in which it was resting. This marks the first outward sign of gall 
formation. On the upper surface of the young leaf the gall appears as 
a shallow depression measuring about 0.5 mm., in depth and in width, 
the margin of which shows a growth of fine upright hairs, while the 
under surface of the gall shows a corresponding convexity as compared 
with the rest of the lower surface. 
Text-figure 4 shows an early stage of gall formation such as de- 
scribed above. The figure was drawn under a binocular microscope 
while the leaf and insect were still living, and shows the insect at work 
on a vein, lying in the depression and surrounded by the hairs, both of 
which are the results of her labor. Rathay (23) gives good colored 
drawings of the outside appearance of these early stages of gall for- 
mation. 
In order to follow the histological development of the gall, dif- 
ferent stages were collected, fixed in various dilutions of Flemming's, 
Carnoy's and other fixatives, imbedded in paraffin and subjected to 
various stains. Nearly all material was cut so as to give a serial ar- 
rangement of sections. 
The first sign of gall formation in 19 14 did not appear until late 
May. Opening buds from any region of a vine showing galls on the 
expanded leaves were brought into the laboratory and examined for 
signs of the grape-vine Phylloxera. Fortunately, I was able to find 
very early stages in great abundance. Figure i shows a cross section 
of a gall which is not more than twenty-four hours old; the hairs 
