ROOT BLIGHT. 487 



III. Diseases AFFECTING THE Stem. 1. Root Blight. 

 This especially affects young dwarf pear trees. Very 

 soon after the trees begin to grow, the leaves and 

 wood turn to a deep brown color, approaching 

 bronze. It differs entirely in appearance from the 

 common pear blight, because that is black, and at 

 first extends only over a portion of the tree ; while 

 this is general, and takes place earlier in the season. 

 On examination, the roots will be found dead, 

 which, in the young dwarf pear, are very near the 

 surface of the earth, and possess no strong taps to 

 keep them in place ; and therefore, in undrained 

 land, when the ground freezes and thaws, the tissue 

 of the root is destroyed by the constant strain. 



2. Insects. (1) The Pear-blight Beetle — Scolj/tus 

 Pyri : Peck. Tomicus Pyri : Harris. " This insect 

 causes a blight of the limbs, which, in its outward 

 appearance, resembles the common pear blight. 

 The limbs which it attacks, turn black, and die in 

 early summer, while other parts of the tree remain 

 healthy. The disease is caused by the larva of this 

 insect, whose eg^ was laid in the axil of a bud, who 

 ate his way inward, and followed the eye of the 

 bud toward the pith. Around this it passes, and 

 partially consumes it. Thus the insect, after pen- 

 etrating through the alburnum, forms a circular 

 burrow or passage in the heart-wood, contiguous to 

 the pith. By this means the central vessels are 



