356 
birches, the coecidiform, or hibernating females, have attained their 
full development and begin at once their duty of reproduction. The 
young larvee soon after having been deposited are directed by their 
inherited instinct, to move at once to the young and tender leaflets 
which are just bursting forth, and settle on the under side in the folds 
or plications between the transverse veins. The continuous irritation 
produced by the sucking of the insects causes the edges of the young 
leaves to curve down, while at the same time the upper surface of the 
leaves between the veins commences to bulge out and gradually forms 
a 
q 
LEILA 
AZ. 
IGE 
& 
SE 2: 
Fic. 19.—Hamamelistes spinosus; Pseudo-galls, or corrugations, on leaves of birch—natural size 
(original). 
rounded ridges, or corrugations, while the folds on the under side 
The thus formed pseudo-galls, offer ample room 
gradually close up. 
These corrugations or folds 
for the gall-makers and their progeny. 
acquire a reddish-brown shade which soon changes to a beautiful red- 
dish or crimson color. The growth of the young insect is rapid, keeps 
pace with the growth of the infested leaves and reaches full develop- 
ment by the end of April or early in May, or about twenty days from 
the time they were born and commence at once to reproduce their 
kind, which frequently become so numerous as to fill these pocket- 
like folds to their utmost capacity. In favorable years the insects 
