g8 
BRITISH GALLS 
a section through three galls and one of the larger veins; 
Fig. io the orifices on the lower surface of the leaf 
(Figs. 8 to io are magnified). There is another common gall 
on Maple leaves caused by Eriophyes macrochelus. It is 
abundantly distinct from the preceding in its larger size and 
isolated habit (Figs, n, 12, 13), and may also at once be dis¬ 
tinguished by the pluricellular character of the hairs which 
line its interior (Fig. 14). The galls of both species may 
occur on one leaf, and leaves quite devoid of galls may often 
be found adjacent to infected ones. Several species of 
supposed Phyllerium have been observed on fossil Maple 
leaves. 
At least three species of Eriophyes frequent Alder leaves in 
this country, causing familiar galls. In those resulting from 
the presence of E. Nalepai the pustules are hemispherical, 
about 3 mm. high, seated on the upper surface, always at 
the junction of the lateral veins and midrib, and arranged 
in pairs. They are glabrous, yellowish-green at first, be¬ 
coming red or brown. Each pustule contains a cavity with 
a wide opening on to the lower surface of the leaf. The 
hairs are white or yellowish-brown; when viewed under the 
microscope they are seen to be of two kinds—one plural- 
celled, blunt-pointed, and thick-walled, usually much dis¬ 
torted and entangled; the other unicellular, very short and 
thick. The slight swellings on these leaves are caused by 
Eriophyes brevitavsus. In the early stages of growth the 
hairs lining the depressions on the lower surface are whitish; 
they become brown at maturity, and resemble, when viewed 
with a pocket-lens, minute crystals of Demerara sugar. 
Under the microscope the crystal-like bodies are seen to be 
the enormously swollen heads of the hairs. In the inter¬ 
stices between these growths the mites live in hundreds, 
browsing upon the “ sugar ” so generously provided for 
them by the plant. The busy colony is a most fascinating 
object of contemplation. It is difficult to realize that the 
remarkable alteration of epidermal cells, from their normally 
flattened shape to these peculiar club-shaped bodies, is 
