The Scottish Naturalist. 373 



THE GALL-MAKING- DIFTERA OF SCOTLAND. 



BY PROF. J. W. H. TRAIL, A.M., M.D., F.L.S. 



(Read before the U.S. Union of Naturalists' Societies, in June, 1887.) 



(Continued from page 328.) 



6 



Populus Tremula (Aspen) has the leaf-stalks galled by Diplosi 

 Tremulce Winn. The galls seldom encroach on the 

 twigs, but often do so on the base of the leaf-blade. 

 Each is rounded, about 6 mm. across, tapering a little 

 above and below, smooth, reddish or yellowish green, 

 with a thick hard wall, and small cavity, occupied by one 

 larva. When the larva is full fed, the gall splits at one 

 side, dries up, and becomes brown and harder. These 

 galls are not uncommon in various places along Deeside 

 (T.S.N., II., 253 ; T.A., L, 68). 



Salix. In this large genus galls have been found in Scotland of 

 at least five species of Cecidomyidce, viz.: 



1. C. Salicis Schrk. (C. gallarum-salicis Hardy, Trans. Bot. 



Soc, Edin., IV., 78-79), which causes fusiform swellings 

 of the twigs, which may be from two to five times the 

 natural thickness. In these swellings the woody tissue 

 is not increased ; but the pith is much enlarged, and 

 contains several cavities, each occupied by a larva ; the 

 surface hardly differs from that of an ordinary twig. 



2. G. rosaria H.Lw. (C. cinerearum Hardy, Trans. Bot. Soc, 



Edin., IV., 78, Scot. Gard., III., 84), causes rosette-galls 

 at the tips of the twigs of the Caprea group of Salix. 

 The leaves remain small, crowded, and sessile ; and 

 surround a small cential space, almost filled with hairs, 

 occupied by larvae. 



3. C. heterobia H.Loew (C. saligna Hardy, Trans. Bot. Soc, 



Edin., IV, 78), either produces rosette-galls on tips of 

 twigs of various willows, or galls the male catkins, which 

 become swollen, hairy, and deformed. Both forms have 

 been sent me from Salix triandra near Perth by Dr. 

 Buchanan White ; and Mr. Hardy records it (as C. 

 maligna) from rosette-galls on S. cirierea in Berwickshire. 



