AMERICAN PEAR BLIGHT. 477 



entirely destroy blocks containing thousands of 

 trees, or leave them to struggle for years against 

 the poison thus introduced. Some varieties are 

 peculiarly susceptible to it, as the Belle Lucrative 

 (Fondante d'Automne), and particularly the Glout 

 Morceau. The latter sort shoots a great many soft 

 twigs, and grows late, unless prevented by summer 

 pinching. 



Blight commonly makes its appearance in districts, 

 more or less extensive, not exposed to any severe 

 sweeps of wind during the season of growth. A 

 gentleman in Western Massachusetts once doubted 

 the truth of this assertion, and said that his orchard 

 had been severely attacked, and yet it was on the 

 top of a hill. It was visited on a stormy day in 

 autumn, when the wind was very severe; but, on 

 entering, the air was calm and still ; for, while the 

 orchard lay open toward the south, at all other 

 points it was skirted by forests. 



The strength of timber grown upon mountains, 

 or in exposed positions, is known to be much greater 

 than that grown in low valleys or on plains, where 

 the air is more or less stagnant. 



Trees growing on the former sites always better 

 endure the severities of winter than those on the 

 latter. As before suggested, the gentle breezes of 

 summer are of immense importance to the tree dur- 

 ing the growing season, supplying the leaves with 

 abundance of carbonic acid, so that the wood be- 



