ATTACKING THE ROOTS. 



233 



wander off through its partly-opened mouth on the upper 

 side of the leaf, and establish themselves either on the same 

 leaf or on adjoining young leaves, where the irritation oc- 

 casioned by their punctures causes the formation of new galls, 

 within which the lice remain. After a time the older lice 

 die, and the galls which they have inhabited open out and 

 gradually become flattened and almost obliterated ; hence it 

 may happen that the galls on the older leaves on a vine will 



Fig. 240. 



be empty, while those on the younger ones are swarming with 

 occupants. 



These galls are very common on the Clinton grape and other 

 varieties of the same type, and are also found to a greater or 

 less extent on most other cultivated sorts. They sometimes 

 occur in such abundance as to cause the leaves to turn brown 

 and drop to the ground ; and instances are recorded where 

 vines have been defoliated from this cause. The number 

 of eggs in a single gall will vary from fifty to four or five 

 hundred, according to its size. There are several genera- 

 tions of the lice during the season, and they continue to 

 extend the sphere of their operations throughout the greater 

 part of tiie summer. Late in the season, as the leaves become 



