12 FRUIT BOOK. 



for the destruction of most insects that infest our 

 trees. The slimy slug, found upon the leaves of 

 our pear trees, may be effectually destroyed by 

 the application of wood ashes, thrown upon the 

 leaves during moist weather. The canker, a dis- 

 ease which injures many trees, causing the bark 

 to grow rough and scabby, and turning the wood 

 into a rusty brown color, is said, by some, to be 

 owing to a stintiness that takes place in the trees 

 from a bad sub-soil. It is thought by Rodgers, 

 from long experience as a cultivator, to be prin- 

 cipally owing to some impure quality in the sub- 

 soil. This theory is, however, different from 

 Forsyth's, who says, that the canker " always pro- 

 ceeds from the branches and stems to the roots, 

 and never from the roots to the tree." Planting 

 high, and in wet soils, even almost to the surface, 

 inducing the roots to take a horizontal direction 

 near the sun and air, is thought to be the best 

 m^ans for preventing this disease. We appre- 

 hend that this disease is often brought on by 

 injudicious pruning, leaving the wounds ragged, 

 and thereby admitting water into the wood, which 

 soon begins to decay ; and also from injuries sus- 

 tained by the bark being bruised by ladders 

 while gathering the fruit. In careless pruning, 

 the dead shoots are often left upon the tree, 

 throughout the summer, which often brings on 

 the canker. The exuding of gum, a kind of 

 gangrene incident to stone fruit, may be owing, 

 in some degree, to injudicious pruning, bruises, 

 or injuries received in the wood or bark, or by 

 cutting the shoots to short stumps in summer. It 

 is often seen where large limbs have been lopped 

 or broken off. Among the insects destructive to 



