116 



CAUSE OF PEAR BLIGHT. 



remainder to a thickness of one-fourth of an inch. The trays 

 should be made one or two inches narrower than the box and 

 ai ranged so that the hot air is driven from front to rear and back 



m 



again as in the sketch, which gives a sectional view of the 

 evaporator. The door is hung at the top as shown, but should be 

 kept closed except when putting in or removing trays. [R. 

 Ferris, Essex county, N. Y. 



THE CAUSE OF PEAR BLIGHT. Col Leighton of Virginia 

 claims that pear blight is caused simply and wholly by sudden 

 changes of temperature. He says, "In the early part of May 

 when the sap is ascending briskly, and cool nights have occurred 

 with warm days, and when the difference of temperature within 

 the 24 hours is about 30 degrees, twig blight appears from eight 

 to ten days thereafter." He feels so sure that a sufficient varia- 

 tion of temperature at this season of the year brings on blight, 

 that he has no hesitancy in predicting the disease by the aid of 

 the thermometer, and the disease actually did appear on May 20, 

 1887, as he prophesied on May 12. 



But at Geneva, N. Y., where I was then located, the thermom- 

 eter showed a variation of 20 degrees between night and day ten 



