64 



BRITISH GALLS 



in shape and position ; we may recall the bean-shaped galls 

 caused by the hymenopteron Pontania pedunculi on Salix 

 capraea and S. cinerea. It is possible that Perrisia ulmariae 

 attacks the Dropwort, piercing the upper surface of the 

 leaf, and that another species, indistinguishable to all 

 appearances from it, attacks the Meadow Sweet, each 

 insect keeping to its particular plant. Allusion has already 

 been made to the highly interesting fact that ten species 

 of gall-gnats which attack Salix humilis in America are 

 practically indistinguishable the one from the other, though 

 each causes a distinctive gall. It may be suggested, there- 



FiG. lo — spiraea FiUpendula galled by Perrisia ulmariae, (i/i.) 

 Fig. u — Section of a Gall, showing Aperture on Upper 



Surface of the Leaf. (2/1.) 

 Fig. 12 — Spiraea ulmaria galled by Perrisia ulmariae. (i/i.) 

 Fig. 13 — ^Section of a Gall, showing Aperture on the Lower 



Surface of the Leaf. (2/1.) 



fore, that Perrisia ulmariae of the Dropwort deserves specific 

 rank under the name oi Perrisia filipendulae. 



The Gerniander Speedwell has a hairy stem, and the 

 under surface of the leaves is covered with short white 

 hairs. The terminal leaves of this very familiar plant are 

 commonly attacked by Perrisia veronicae (Plate VIII., Fig. 2, 

 magnified). The leaves become folded upwards and the 

 hairs are abnormally developed, forming a gall which looks 

 very like a bunch of white hairs (Plate VIII., Fig. i). It 



