GALLS CAUSED BY SAW-FLIES 
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(b) Unilateral rounded swelling, attaining the size of a 
small nut ( Cryptocampus medullar ins). 
Leaf Galls 
(a) Petiole with fusiform swelling, 2 mm. in diameter ; 
sometimes the base of the midrib is involved ( Cryptocampus 
venustus ). 
( b) Margin loosely rolled inwards ( Pontania lencosticta, 
P. scotaspis, P. viminalis). 
( [c ) In the blade, showing on both surfaces— 
(i.) Elongated swelling {Pontania femoralls). 
(ii.) Smooth, bean-like, greenish or brown [Pontania 
vesicator). 
(iii.) Often corrugated, red, reniform [Pontaniaproximo). 
[d) On the under surface of the blade— 
(i.) Glabrous and spherical [Pontania salicis ). 
(ii.) Hairy and spherical [Pontania pednnculi). 
The best known of all the saw-fly galls on Willows is that 
caused by Pontania proximo , perhaps better known to British 
cecidologists under the name of Nematus gallicola. The leaf 
buds are attacked in May. The larva is at first white and 
transparent-looking, with a shining blackish head. It soon 
becomes green. At maturity the head has a greenish-white 
semicircle on the face. The pupa is white. These galls are 
often very abundant in June and July on many species of Wil¬ 
lows. As a rule, there are two or three on a leaf (Plate II., 1), 
but occasionally there are as many as six. It is the excep¬ 
tion to find a gall on the apical third of the leaf. In its 
early state the gall is almost solid, excepting a little space in 
the centre containing the egg. It usually appears almost 
equally on both surfaces of the leaf. The larva feeds 
around the interior, and by the time it is full fed the gall is 
a mere shell. The gall is yellowish-green at first; later it 
takes on a red tint, which is always more pronounced on 
the upper surface, and most vivid in leaves fully exposed to 
