DISEASES OF CULTIVATED PLANTS 349 
With shade trees the leaf hoppers and mites may be so numer- 
ous that tip-burn and various leaf dying results from the injuries or 
punctures they inflict. 
A more startling relation is that of the blade blight of oats, a 
recently investigated bacterial trouble. 
This bacterium is distributed and 
inoculated very obviously by the 
aphids or green flies (plant lice), and 
other sucking insects which prevailed 
during the seasons of 1907 and 1908 
upon oats almost throughout Ohio. 
For fuller details see Blade Blight 
under Oats, and Bulletin 210. 
WOUNDS AND WOUND INFECTION 
With woody growths, especially 
in trees which attain considerable size, 
we have the various phenomena of 
disease infection through wounds; this 
infection later becoming evident by 
reason of decays set upin the woody 
tissues. Of course, in instances such 
as the bark disease of the chestnut, 
Diaporthe parasitica Murr., the dis- 
ease may penetrate the living tissues. 
Not so, generally, in wounds of woody 
plants. Any large woody growth, as 
in forest or shade trees and in larger 
fruit trees, shows the combination of 
an external or living sapwood layer Wiget Reel atone 
and an internal dead or _ heart- — with large branch cut off. Below this 
wood cylinder. The commoner forms  jytinay nas ja yen Ani 
of wound infections are attributable cap is nine inches across. This shade 
to those species of fungi which cause are ns Ome eee 
decay of this dead heartwood. Among pole. (From a photograph by J. M. 
these are the long list of saprophytic, S"*e"” 
agarics, polypores and stereums. Because of the fact that this 
heartwood cylinder is dead, these saprophytic species of fungi, once 
they gain entrance into it, flourish there and invade the wood toa 
very great extent, even by adaptation to parasitic habit extending 
their work into the living parts causing death. The removal ofa 
large branch of a shade tree or a fruit tree, unless the wound thus 
