1881.] Bacteria as a Cause of Disease in Plants. 531 
sudden appearance often noted is but the blackening of the 
leaves upon a branch long diseased. 
The slow progress of the malady gives the best hope for suc- 
cessful treatment. It has been considered sudden and irregular, 
with little or no indications of trouble until destruction came; 
but this is greatly over-stated. Acquaintance with the first ap- 
pearance in the bark, and careful examination every two or three 
weeks, will make treatment much more possible than heretofore 
supposed. The remedy proposed is the old one of cutting away 
the diseased portions, adding, however, the precaution of taking 
all infected parts, and not merely such as have become blackish 
after the ravages are complete, and to observe requisite care in 
cleansing the knife or other instrument, that by the very process 
of cure the contamination is not spread. Probably carbolic acid 
or other antiseptic washes may be useful, but proof from ac- 
tual and indisputable experiment has not yet been reached. 
Very recent examinations of material sent from Michigan con- 
clusively confirms my opinion that the yellows of the peach tree 
is caused by a similar organism. In the cells of an infected shoot 
I find very little stored starch, but numerous bacteria. These are 
seemingly different, under a one-tenth Tolles’ or Spencer’s objec- 
tive, from the bacteria of the pear and apple. Compared with the 
latter, they are long and slender, measuring about .oor mm. by 
0035 mm. They consist of several joints, but little longer than 
wide in what appears to be the typical forms. 
The Lombardy poplar trees are also destroyed by these fer- 
ment producing agents, following the attacks of certain wood- 
boring coleopterous larve. The latter penetrate the bark and take 
devious courses through the bark parenchyma and the cambium 
layer, Starting from their channels, the bacteria slowly spread 
from cell to cell, until so much of the essential tissue is destroyed 
that the tree, after some years of hopeless struggle, succumbs. 
Sometimes the bacteria collect in immense numbers in pockets, 
which they appear to form in the bark of this tree by absorption 
of the cell walls, The thick, white mass which they thus form, 
has the appearance to the unaided eye of pus from sores in the 
flesh of animals. 
_ The aspen (Populus tremuloides) is similarly affected. The 
young limbs die and the leaves become black in a manner every 
Way similar to those of the pear and the apple. 
