HEMIPTERA. l6l 



the vine. Carbon bisulphide has been used to some extent 

 for this purpose. 



Where the vineyards are so situated that they can be 

 submerged for a period of at least forty days during the 

 winter, the insect can be drowned. But this method is 

 obviously of limited application. 



It is found that vines growing in very sandy soil resist 

 the attacks of the Grape Phylloxera. This is supposed to be 

 due to the difficulty experienced by the insect in finding 

 passage through such soil. 



Another well-known example of the plant-lice that make 

 galls is Colopha uhnicola (Coro-pha ul-mic'o-la), which makes 

 the Cockscomb Elm-gall. This gall is shaped more or less 

 like a cock's comb, and is very common on the upper side of 

 the leaves of the elm. 



There is a group of species of plant-lice known as the 

 Woolly Aphids, on account of a white more or less downy 

 or waxy substance with which the bodies of these insects are 

 covered. Large numbers of one of these species are often 

 found crowded together on the under side of the branches of 

 alder. This species is known as the Alder-blight, Schizoneura 

 tessellata (Schiz-o-neu^ra tes-sel-la^ta). In addition to the 

 white excretion with which^the body is covered this insect 

 excretes large quantities of honey-dew. The result is that 

 the branches infested by this insect, and those beneath the 

 clusters of Aphids, become blackened with fungi that grow 

 upon this secretion. There is also a curious fungus which 

 grows in large spongy masses immediately beneath the clus- 

 ters of plant-lice ; this is known to botanists as Scorias 

 spongiosum. It is evidently fed by the honey-dew that falls 

 upon it. 



The Beech-tree Blight, Schizoneura imbricator (im-bri- 

 ca'tor), infests both the twigs and leaves of beech. Like 

 the preceding species it occurs in clusters of individuals, 

 each of which is clothed with a conspicuous downy excre- 

 tion. These clusters often attract attention by the curious 



