108 The Scottish Naturalist. 



plants were introduced in a condition {e.g., as seeds, by birds) not suited 

 for the introduction of the gall-making insects. It is, however, im- 

 possible now to discover the special cause of immunity in the case of 

 each of such plants, and we must be content, in most cases, to record the 

 bare facts, leaving the explanations of these facts unattempted. 



To complete the account of the galls of Scotland, those caused by 

 Fungi ought also to be ranked alongside of those of animal origin ; 

 and I hope to make the former galls the subject of a future paper. 

 Meanwhile, I shall confine my remarks to the latter, in completion of 

 my former papers in this Journal. 



Galium uliginosum L. I have recently found on this plant, near 

 Aberdeen, galls of the same nature as those produced by mites (Phytop- 

 tus), on various other species of Galium, e.g., on G. Aparine (Sc. Nat. 

 IV., p. 15, b.), on G. saxatile (I.e.), and on G. palustre (Sc. Nat, N. Ser., 

 I., p. 210, b.) Like the latter galls, they are leaves convoluted or 

 rolled from the tips so as to form shelters for the mites. In colour 

 they hardly differ from the healthy leaves. On all the species of 

 Galium, they are probably the work of the same species of mite. 



Sonchus arvensis, L. On a few small plants of the Sow-thistle, at 

 Gamrie, a few miles east of Banff, I found on 20th August, 1886, 

 several galls of Cecidomyia Sonc/ii F. Loew (V. Bot. Zool. Ges. Wien, 

 1875, P- J 8). They resemble blisters of the epiderms of the leaf, being 

 raised a little in a very low cone above the general level, especially on 

 the upper surface. Looked at from the surface, the gall is pale 

 yellowish or reddish-green, surrounded by a dark purple-red ring, and 

 is about 5mm. (iinch.) in diameter. On section it is found to have 

 the lower wall very thin, and pierced by a minute opening ; this wall 

 is the lower epiderm of the leaf, separated from the middle tissues. 

 The upper wall includes the latter tissues ; and is therefore thicker. 

 The chamber between the two is lenticular, and is occupied by a yellow 

 larva which, when full-fed, becomes a pupa, in a small white cocoon 

 in the gall. I was unfortunately unable to rear the Midges, but the 

 galls agree completely with Dr. Low's description, so as to leave no 

 doubt that they are to be ascribed to G. Sonchi. Often a number of 

 galls (over a dozen,) are crowded on a leaf, especially on the leaves 

 near the base of the stem. 



Fraximis excelsior, L. (Ash). I have already descfibed (a) the 

 galls on mid-ribs of the leaflet of the Ash, produced by Diplosis 

 botularia Winn, (Scot. Nat. I, p. 158, and II, p. 252). (b) In August 

 1886, I found, near Banff, a number of leaf-galls in the leaves, which 

 in nature and structure much resembled those just described from 

 Sonchus, consisting of blister-like swellings of about the same size as 

 the latter but they hardly differed in colour from the rest of the leaf, and 

 only from one to three occurred on each leaflet. Most of them were 

 empty ; but in one or two I found a whitish or yellowish larva, appar* 



