1178 Pear Blight and its Cause. [ December, 
it would be a matter of considerable difficulty to describe it in 
such diagnostic terms that the reader would recognize it under 
all conditions and avoid confounding it with the numerous other 
blights and incidental maladies which resemble it. Its most 
characteristic feature, if one considers only pomaceous trees, such 
as the pear, apple, quince, crab, hawthorn, etc., is the complete 
dying of the branches subsequent to the appearance of the foli- 
age without obvious cause and usually with apparent suddenness. 
This involves the limb and its leaves, both of which turn blackish 
and usually exhale a peculiar but not very strong odor. From 
the softer stems there often exudes a viscid, whitish substance 
forming small drops on the surface of the bark and finally becom- 
ing hard like an exudation of gum. 
The blackening of the dying branches does not differ from that 
produced by death from other causes; hence arises the danger of 
mistaking other injuries of the tree for the true blight as here 
understood. Death may be brought about by the limb being 
partly broken off, or it may be punctured and killed by the pear- 
blight beetle (Xyleborus pyri), a very small insect which often 
escapes detection, or it may result from other mechanical injuries. 
There is also the blackening of the ends of young twigs in spring 
known as frozen-sap blight, the blackening of the edges of the 
leaves later in the season, more common on some varieties, 2. £., 
the Sheldon, than on others, and so on. But the real blight kills 
the limb in advance of the leaves, and will usually show the 
blackened bark, when raised with a knife, below the lowest dead 
leaves; the gummy exudation, when that is to be found, is abun- 
dant confirmation. In addition to this, the extent of the malady, 
sometimes embracing the larger part of the tree and most of the 
trees of the orchard, assures one of its identity. Pear leaves may 
at times assume a deeply bronzed appearance and the bark be- 
come dark colored, but these appearances need never be mistaken 
e _ for blight, as the tissues beneath will be found normally green 
_ The disease is most observed during July and August. It may 
manifest et upon any part of the tree, but starts rather more 
. 
is not coed the disease will eee 
e trunk pi: the tree. It is purely a local disease, 
