242 



StICKING INSECTS. 



Black Blight. — Plants infested with these insects often have a black 

 coating on their leaves commonly called " Black Blig'ht "; this is often 

 mistaken for the real disease. This black coating is the result of the work 

 of the insects ; they snck a great quantity of juice from the plant and in 

 turn a sweet fluid (honey dew) drops from them upon the leaves below ; 

 as this dries it becomes sticky and then a mould {CapnocUmn) grows in it 

 Avhich, being black, gives the plant a black appearance. This mould 

 (similar to that which comes on boots, etc., in the rains) does little harm 

 and does not penetrate the tissues of the plant. The black must be traced 

 to its right cause, the insects ; when these are killed the mould will cease. 



Scale Insects and Mealy Bugs (Coccidse). 



A class of pests distinct from all others are formed by the insects 

 generally known as Scale Insects and Mealy Bugs. They arcj found 



Fig. 290. 

 Red-spotted Scale, a, natural size, h, female scale, c, male scale, i, female, e, male. 



as small scale-like insects, usually thickly infesting the leaves, twigs or 

 bark of the plants they attack. Many are covered with distinct scales, 

 formed of special wool-like niatcriiil mixed with the cast skius uf the 



