8 Blight in Apple and Pear Trees. [July, 



to trace the death to a satisfactory cause, and our verdict on a post 

 mortem examination must be, death from girdling. 



The late Prof. Peck, as is well known, discovered the cause of 

 one species of blight, in the insect called the Scolytus pyri, which 

 eats around the branch beneath the bark. 



This kind of blight must necessarily be distinguished from the 

 blight which we have described, and which we consider a true 

 vegetable gangrene. The remedy may be the same, viz., extir- 

 pation. In the one case extirpation is performed for the purpose 

 of destroying the destroyer; in the other, it would seem for the 

 purpose of preventing the mingling of tainted fluids with those 

 which are healthy, and by which it is to be feared the disease may 

 be extended to the whole system. In support of this view of the 

 matter, it may be observed that it is an established fact that the 

 contact of diseased parts with sound ones, or the mingling of dis- 

 eased fluids with the healthy, is invariably injurious; and that un- 

 der such circumstances the disease propagates itself in a manner 

 which may be likened to the efl"ects of leaven. This, it is true, is 

 one of the* oldest ideas of cause in accounting for diseased or un- 

 healthy action, though of late it has been brought before the pub- 

 lic in a dress somewhat new. As we are now speaking of the 

 cause of blight, it is but right that we should refer to a cause 

 which has been assigned by a distinguished writer upon horticul- 

 ture. The writer referred to maintains that it is caused by sap 

 which has frozen during the preceding winter. 



There are many objections to this as a cause of the blight here 

 described. 



1. If the sap is frozen, and is thereby changed in its proper- 

 ties, it can hardly be maintained that it is capable of perform- 

 ing the part of a nutritious fluid, and possess the required proper- 

 ties which shall fit it for the development of leaves. It is but 

 rational to infer that sap, when changed essentially by any cause, 

 should act in the first period of its circulation in its usual way, 

 and then subsequently, after having performed the exact purpose 

 of healthy sap, at last can cause the death of a part which it had 

 brought "into life and existence. Besides, it is no where shown 

 that frozen limbs always result in their destruction, or in the de- 

 struction of the sap. Repeated freezing and thawing will un- 

 doubtedly destroy the vegetable organs, but in these instances the 

 effect is immediate, and the limb or tree never puts forth its leaves 

 at all. In the county of St. Lawrence, and in ether parts of the 

 state, where frost destroys a tree or a part of it, there is an entire 

 end of it. It never exhibits a vigorous life, it never puts forth 

 strong and healthy leaves and blossoms, but it is actually a dead 

 tree, or a dead part, when the cause has thus acted upon it. 



2. It is agreeable to all that we know of the effects of freezing 



