The Blight in Pear Trees. 21 



The diminished supply of sap would affect the whole limb 

 above the point of attack, and would not cause a shrivelling 

 of the bark, in girdling rings, or in patches, at the base of the 

 limb, or midway of its length. If the bark and limb remain 

 in good condition, as this hypothesis of insect blight concedes, 

 the nev/ wood would be formed continuously down, and a 

 ready means furnished for the sap to ascend the next year, so 

 as to produce restoration. It will always be found, that the 

 new wood is abundantly deposited along the whole length of 

 limb and trunk, above the point of injury, and many times 

 vigorous efforts are visible, to throw down a new column over 

 the injured part. JMr. Lowell's conclusion, as to the cause of 

 blight, was not sound, and the authority of his great name 

 has caused it to pass unquestioned. 



Dr. Harris is also referred to as a concurring authority for 

 the hypothesis of insect blight. His book on insects con- 

 tains the following: — " From Mr. Peck's account, and from 

 the subsequent communication by Mr. Lowell, in the 5th 

 vol. of New England Farmer, it appears that the grub or 

 larva of the insect, (Scolytus Pyri,) eats its way inward 

 through the alburnum or sapwood, into the hardest part of 

 the wood, beginning at the root of a bud, behind which, pro- 

 bably, the egg was deposited, following the course of the eye 

 of the bud, towards the pith, around which it passes, and 

 part of which it also consumes, thus forming, after passing 

 through the alburnum, a circular burrow, or passage in the 

 heart-wood, contiguous to the pith which it surrounds. By 

 this means, the central vessels, which convey the ascending 

 sap, are divided, and the circulation cut off. This takes 

 place when the increasing heat of the atmosphere, producing 

 a greater transpiration from the leaves, renders a large and 

 continued flow of sap necessary to supply the evaporation. 

 For the want of this, or from some other unexplained cause, 

 the whole of the limb, above the seat of the insect's, opera- 

 tions, suddenly withers and perishes, during the intense heat 

 of mid-summer," (p. 75). Those who quote him omit to give 

 Dr. Harris's cautious qualification, that, for want of sap, 

 or from some other unexplained cause, the limb perishes. He 

 evidently had an involuntary doubt of the theory he copied. 



I may also add, that the blight of 1826 caused many pub- 



