304 The Scottish Naturalist. 



Betula alba L. — (b) The gall consists of a swelling of the 

 midrib, most conspicuous below, and including the origins 

 of the chief veins. When dry, it is light brown (dark at 

 first), nearly smooth, and naked. It is usually nearly cylin- 

 drical, but pointed at each end, and measures about J 1 ; 2 ' by 

 g'. Each contains one whitish larva. Dunkeld, Parkhill, 

 Braemar, and Strathnaver (in Sutherland), (c) Consists of 

 a blister of the lamina projecting both above and below, so 

 as to inclose a cell. It is usually connected with the mid- 

 rib, or with a large vein. In shape it is usually oval, Jf ' by 

 Jf' when single, but frequently two or more are united. 

 The surface is covered with short hair like the rest of the 

 leaf. The gall is green in the centre, and purple round the 

 sides. The walls are thin ; the central cavity large. Each 

 is tenanted by a larva of Cecidomyia, which, when mature, 

 emerges through the lower surface. Common in July and 

 August at Parkhill, Fyvie, Braemar, Sutherlandshire, etc., 

 chiefly on bushes, (d) On the same bushes with the last, 

 the buds at the tips of the branches were frequently swollen, 

 and were always in such cases inhabited by the larvae of 

 Cecidomyia, possibly the same as the last. 



Alnus glutinosa L. — Both the galls on this tree described by 

 me are formed by Phytopti (four-footed mites). Both are 

 abundant everywhere, even to Orkney. 



Pinus sylvestris L. — The galls of Oribata geniculata have 

 already been commented on by Mr. Norman (Sc. Nat., I. 

 55). They form rounded swellings on the twigs, J' to J' in 

 diameter. Internally they are compact, and woody in the 

 centre, with a layer of loose cellular tissue surrounding this, 

 and in the cellular tissue are cavities in which dwell the 

 mites, Oribata geniculata. Sent me from Dunkeld by 

 Dr. Buchanan White. I have found them near Ballater, 

 and near Inverury. 



Pteris aquilina L. — The galls on this plant consist of the 

 ultimate pinnules, the margins of which are revolute and 

 fleshy. Sometimes one margin is affected, sometimes both. 

 At first the colour is only a little yellower than natural, but 

 ultimately it becomes yellow, and passes then through vari- 

 ous shades of brown to black. Each is tenanted by one 

 larva of Cecidomyia ptcridis Mull., which drops to earth 

 when mature. About Aberdeen, and at Lintrathen, Dun- 

 keld, etc. 



