530 Bacteria as a Cause of Disease in Plants. [July, 
The following table gives the results in per cents of the number 
of successful inoculations: 
Tah ccsescid Kinds of Trees. = _— Virus from Apple. 
36 Pear 54 72 
29 Apple 30 Not tried. 
4 Quince 100 Not tried, 
It will be observed that the virus from the diseased apple limbs 
was more fatal to the pear than that from blighting pear, showing 
at least that the disease in the apple is of the same nature as that 
known as fire blight in the pear. It is quite possible, however, 
that the greater percentage is due to other causes than the viru- 
lence of the inoculating material, and that another set of experi- 
ments would show this. The low per centage in case of the ap- 
ple (30) inoculated with pear virus is partially explained from the 
fact that ten inoculations were in the bark of portions more than 
one year old, none of which were successful. As these trees show 
blight for the most part in the shoots of the current year’s growth 
only, some reason for the failure may be conceived. But four in- 
oculations were made in the quince, all of which communicated 
the disease. These were made upon the young shoots of a bushy 
tree which was not otherwise unhealthy. 
Since these experiments were made, careful study has com 
vinced me that the death of patches of bark on 
d oe. & Be the trunk and larger limbs of the apple tree #8 — 
09 vcs due to the same cause. The disease slowly pro- 
Hie 8 gresses from the center of infection and kills the 
gas 8 i: ye tree when the whole circumference becomes 1 
Peg ge volved. Sometimes, however, the liber (the bast 
oom os cells are not penetrated by the bacteria) forms 4 
Blight Bacteria. complete shield to the inner tissues, and after the 
Magnified rooo outer cellular bark is destroyed a new layer 1S 
formed beneath, the old finally falling away- 
Meteorological conditions probably have some influence, but 
how much and what is not clear. The disease slowly progresses 
in winter as well as summer, in dry weather as well as wet, The 
