22 
BRITISH GALLS 
sunlight. At an indefinite time in its growth the larva eats 
a round hole at one end of the gall, from which it ejects the 
frass. Occasionally it leaves its home, but never for long. 
The hole is always on the under side of the leaf, and 
almost invariably in that end of the gall which is towards 
the tip of the leaf. (See Fig. i a in Plate II.) Fig. 2 depicts 
a magnified gall, and Fig. 3 a transverse section. It never 
opens directly upon the leaf surface, but is directed slightly 
upwards. Sometimes the egg is misplaced ; the gall arises 
at the extreme edge of the leaf margin, and is abortive. 
The white cocoons are usually spun in the earth, but some¬ 
times the larvae take advantage of the chinks in the bark of 
old Willows and pupate in them, occasionally many together. 
Cameron observes concerning these galls that “ the cells 
adjacent to the epidermal layer are filled with chlorophyll 
granules, which give to this part a green, granular appear¬ 
ance. Near the centre the cells are paler, more irregular, 
contain apparently less chlorophyll and more intercellular 
spaces. When the galls are young the cells are not so 
irregular as they are later on—in fact, at first they do not 
differ much from the ordinary cells of the leaf.” 
Pontania salicis (it is burdened with many other names*) 
causes rounded glabrous galls on the leaves of Salix purpurea 
and other smooth-leaved Willows. The insect (magnified) 
is shown in Plate II., Fig. 8. Each gall is about 8 mm. 
in diameter, seated on the lower side of the leaf (Fig. 9), 
its presence being indicated on the upper surface by a 
rounded reddish-yellow spot (Fig. 10), not infrequently 
margined with lemon-yellow discoloration, especially 
towards the apex of the leaf. It is green at first, becoming 
yellow, and sometimes reddish, at maturity, and is joined to 
the leaf by a point. There is no hole for the expulsion of 
the frass. The surface is sometimes tuberculated. Fig. n 
is a magnified section of a gall. 
The gall caused by Pontania pedunculi on the Goat Willow 
is of similar size, and also occurs on the under surface of 
* E.g., Nematus gallarum and N. salicis-cinereae. 
