BTJD-GALLS. 547 



gives rise to on Veronica chamcedrys, and which gall-mites produce on the Wild 

 Thyme (Thymus Serpyllum; see figs. 360* and 360 ^ p. 531), form white buttons 

 on the ends of the shoots which show up conspicuously from the dark green 

 of the surrounding foliage. The white colour is due to the fact that the outer 

 leaves, which fold together like mussel-shells, are thickly covered on the outside 

 with white hairs. Gecidomyia Artemisice produces on the branches of Artemisia 

 campestns a closed cluster-gall which is cased in white wool like a shroud. On 

 the other hand, the large, button-shaped, closed cluster-galls which are produced 

 by Gecidomyia rosaria on Willows (Salix purpurea, &c.) and by a gall-mite on 

 the spikes of the Brome-grass (Bromus) are green and smooth, or at least they 

 have not more than the usual number of hairs. 



On the shoots of the Yew (Taxus haccata), the Flax (Linum usitatissimum), 

 JEvphorbia Gyparissias, the Moss Campion (Silene acaulis), and several Ericas 

 (Erica arborea, carnea, &c.) the influence of various gnats (Gecidomyia Taxi, 

 EuphorbicB, JSricce, scoparice, &c.) produces galls with linear erect leaves crowded 

 together into tufts. The base of the crowded leaves and the axis of the gall are 

 usually rather thickened, so that it looks as if the linear leaves were set on 

 a rounded button, and this is particularly marked in Euphorbia Gyparissias. 

 This division includes the gall formations occurring on Juniper twigs (Juniperus 

 communis), which are caused by the gall -gnat Lasioptera junipervna. The 

 acieular leaves of the Juniper are arranged in whorls of three on normal shoots. 

 By reason of the influence of the gall-gnat Hormomyia juniperina the whorls 

 at the top of the twig become so changed that the last but one represents a cup 

 bordered with three teeth in consequence of the broadening of the needles, while 

 the terminal whorl is metamorphosed into a dwelling surrounded by three short 

 leaflets. This gall closely resembles the cone of the Arbor Vitse (Thuja occidentalis, 

 orientalis, and plicata) in form. 



An insect, Livia Juncorum, produces galls on various Rushes (Ju/ncus), espe- 

 cially Juncus alpinus and lamprocarpus, which look like knots or tassels. The 

 axis of the shoot is contracted, the sheathing portions of the leaves which cover 

 one another are much widened, and the colour is pale except where it is reddened 

 by exposure to the sun; their appearance is like the outer covering or top of 

 a tassel. The stunted green blades which spring from the sheathing portions 

 are thread-like and arranged as the loose strands of the tassel. Not infrequently 

 short lateral shoots arise in the axils of some of the leaves, and then the whole 

 structure looks like a bunch of tassels. 



Closely allied to these cluster-galls on the stems of Eushes are such as re- 

 semble tufts and witches' brooms, produced by mites on the branches of hairy 

 Willows, especially on the white Willow (Salix alba). Instead of the long leafy 

 Willow rod which would have emerged under ordinary circumstances from a 

 foliage-bud, a confused mass of twigs with short leaf-scales is developed which 

 at first seems a perfect mystery. By careful examination it is seen that the 

 axis of the shoot laid down in. the bud has remained stunted, and that lateral 



