HEMIPTEEA. 121 



they leave their mother. The young ones set off and mount or 

 descend till they reach one end of the crowd, and there each 

 takes up its position, like a cardboard capucin (capucin de carte), 

 in such a manner that the head is just behind the plant-louse 

 which precedes it. There they bury their trunks in the vegetable 

 tissue, and set to work to imbibe the sap. 



Small as is the trunk of the plant-louse, yet when there are 

 thousands of those little beings fixed to the stalk or the leaves of 

 a plant, it is evident that it must suffer. And so the plant- 

 louse is, in truth, one of the most terrible enemies of our agricul- 

 tural and horticultural productions, and the exact list of the 

 ravages which it occasions would be indeed interminable. We 

 will confine ourselves to a few examples. For some years 

 the lime-tree aphis has seriously attacked the lime-trees of the 

 public promenades of Paris. The peach-tree plant-louse 

 causes the blight of the leaves of that tree. It is to these 

 prolific little parasites that are due, in a great number of cases, 

 the contortions of leaves and of the young shoots of trees of all 

 species. 



These insatiable depredators cause sometimes a still more re- 

 markable alteration. On the leaves of elms one sees often bladders, 

 round and rosy, like pommes d'api. On opening these bladders 

 one finds that they are inhabited by a species of aphis. On the 

 black poplar grow galls of different kinds, some from the leaf 

 stalks, and others from the young stems. They are rounded, 

 oblong, horned, and twisted in a spiral. Other galls show 

 themselves on the leaf itself. They are all inhabited by plant- 

 lice, differing from those of which we have given a descrip- 

 tion above, in the extremity of their abdomen not presenting 

 the two remarkable horns to which we shall have later to call 

 the attention of the reader. The body is generally covered 

 with a long and thick down. 



Of this genus, the species, alas ! so unfortunately celebrated is 

 the Apple-tree Aphis (Myzoxylus mali), which attacks that tree. 

 This insect is of a dark russet brown, with the upper part of the 

 abdomen covered with very long white down. Its presence was 

 announced for the first time in England in 1789, and in France, 

 in the department of the C6tes-du-Nord, in 1812. In 1818 it was' 



