pores of the bark of a black ferruginous appearance ; this happens 

 throughout the whole course of the warm season — more frequently in 

 weather both hot and moist." So wrote William Coxe in a book on the 

 "Cultivation of Fruit Trees," published in 1817, which is said to be 

 the oldest American book on fruit culture. 



Nearly forty years before this we have a record of the disease 

 mentioned in a letter written by one William Denning, who first saw 

 the disease in the Highlands of the Hudson, in 1770. He described 

 the disease fairly well, and thought it was due to a borer in the trnnk 

 of the tree. 



From 1817 to almost the present time, we find in horticultural 

 literature many theories as to the cause of the blight. It would be 

 tedious to give an account of all the different theories put forward by 

 various writers during ihis period. The most diverse views were 

 entertained as to the cause of the disease, and it was a constant topic 

 for discussion in the horticultural journals and societies. These dis- 

 cussions were so wearisome and so barren of results that the Western 

 New York Society resolved that the subject should not be discussed 

 at their meetings unless some one had something entirely new con- 

 cerning the disease to communicate. 



Amongst the different theories put forward to explain the cause 

 of pear blight, we may mention the following : 



1. Insects. 



2. Rays of the sun passing through vapors. 



3. Poor or deleterious soil. 



4. Violent changes of the temperature of the air or the moisture 

 in the soil. 



5. Sudden change from sod to high tillage resulting in surfeit or 

 overplus of sap. 



6. The effects of age ; old varieties being most subject to it. 



7. Autumn freezing of unripe wood, which engendered a poison 

 which destroyed the shoots and branches in the following season. 



8. Electricity, or atmospheric influence. 



9. Freezing of the sap, or freezing of the bark. 



10. The heat of the sun assisted by rain-drops acting as lenses 

 causing the scalding of the sap and bursting of the cells. 



11. Fermentation of the sap. 



12. The absence of certain mineral matters in the soil. 



13. An epidemic transmitted from place to place by the air. 



14. Fungi. 



