CH. X.] THE PLANT-LOUSE. 181 



in the open air have been discovered, wnich are not 

 encased in a downy stuff. 



The injury inflicted by the aphis maybe estimated 

 from the following- extract : " Our apple-trees here 

 are greatly injured, and some annually destroyed by 

 the agency of what seems to be a very feeble insect. 

 We call it from habit, or from some unassigned 

 cause, the ' American blight' (aphis lanata) ; this nox- 

 ious creature being known in some orchards by the 

 more significant name of 'white blight.' In the 

 spring of the year a slight hoariness is observed upon 

 the branches of certain species of our orchard fruit. 

 As the season advances, this hoariness increases, it 

 becomes cottony, and towards the middle or end of 

 summer, the under sides of some of the branches 

 are invested with a thick, downy substance, so long 

 as, at times, to be sensibly agitated by the air. Upon 

 examining this substance, we find that it conceals a 

 multitude of small, wingless creatures, which are 

 busily employed in preying upon the limb of the tret; 

 beneath. This they are well enabled to do by means 

 of a beak terminating in a fine bristle ; this being 

 insinuated through the bark, and the sappy part of the 

 wood, enables the creature to extract, as with a sy- 

 ringe, the sweet, vital liquor that circulates in the 

 plant. This terminating bristle is not observed in 

 every individual : in those that possess it, it is of 

 different lengths, and is usually, when not in use, so 

 closely concealed under the breast of the animal, as 

 to be invisible. In the younger insects it is often 

 manifested by protruding like a fine termination to 

 the anus ; but as their bodies become lengthened the 

 bristle is not in this way observable. The alburnum 

 or sap wood, being thus wounded, rises up in excres- 

 cences and nodes all over the branch, and deforms 

 it ; the limb, deprived of its nutriment, grows sickly ; 

 the leaves turn yellow, and the part perishes. Branch 

 after branch is thus assailed, until they .all become 

 leafless, and the tree dies. 

 L-Q 



