476 DISEASES WHICH AFFECT THE PEAR. 



— Veneficium. Plants, in common with animals, 

 are sensitive to the influence of poisons. These 

 may enter the plant through the root by solution, 

 as the power of selection in the root is, to a degree, 

 limited, or through the stomates of the leaf, as a 

 gas. Many substances, poisonous or not, affect plants 

 and animals in a similar manner. A twig of the 

 sensitive plant was placed in a glass tube which 

 contained sulphurous ether; it soon unfolded, and 

 could be handled without recoiling in the least ; but, 

 through the influence of the external air, it grad- 

 ually resumed its former character. The specific 

 characters of poison may be as different as the 

 number of substances which are poisonous, and the 

 species of plants which they affect. The vicinity 

 of gas-works, and that of some chemical works, are 

 generally considered as unhealthy for plants ; yet 

 it would be impossible, except in a monograph, to 

 describe, even if it were known, all the different 

 effects produced, and state remedies for them. 



■ §m. — DISEASES OF THE PEAR. 



I. Diseases which affect the Foliage. 1. Amer- 

 ican Pear Blight — Effusio subcutanea. There have 

 been a variety of conjectures relative to the origin 

 of this disease. In this country it is the worst 

 malady with which the cultivator of the pear has 

 to contend. Sometimes, entering a nursery, it will 



