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. la 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 saUcis (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. 1 1 

 is a magnified section of a gall. 



The gall caused by Pontania peduncuK on the Goat Willow 

 is of similar size, and also occurs on the under surface of 

 * E.g., Nematus gallarum and N. salicis-cinereae. 



