1896.] The Bacterial Diseases of Plants: 801 
and make their way into the surrounding tissues, first isolat- 
ing and then destroying the parenchymatic cells and finally 
Increasing to such an extent that the epidermis is ruptured 
and a viscid, yellow ooze escapes. The vessels of the scape 
are filled in the same way, but the bacterial slime was not ob- 
served in the roots. The bacteria may be distinguished in 
the vessels considerable distances in advance of any external 
or macroscopic symptoms. The bacterial mucilage is a yellow 
liquid, thick and viscid. Under a low power of the micro- 
scope it shows a granular structure, this being due, as we 
recognize on higher magnification, to the presence of bacteria. 
Dr. Wakker describes at some length his method of examina- 
tion: “The transverse sections must be made with extreme 
care, such as is almost unknown in the ordinary study of veg- 
etable anatomy. Not only is the affected tissue so soft that it 
is impossible, in a fresh state, to cut sections sufficiently thin, 
but there is also danger that the mucilage will be dragged by 
the knife into parts of the leaf where originally there was not 
a trace of it. To overcome these two difficulties good use was 
made of absolute alcohol. The green color was removed by 
this method while the yellow of the mucilage persisted, and, 
in consequence, became much more distinct, so that it was 
easier to distinguish diseased from healthy tissues.” 
(5) Direct Infection Experiments.—This disease was studied be- 
fore Koch’s plate method of isolation had come into general 
use, and most of the infection experiments were made directly 
from diseased to healthy plants. In the fall of 1882 bacteria 
were introduced into a bulb of the double white Anna Maria, 
and when this bulb was cut the next spring it showed distinct 
signs of the disease. This experiment was frequently repeated 
and always with the same result. For example, the whole cut 
surface of the scales of a bulb from which roots and leaves were 
cut away in summer was smeared with the bacterial slime, and 
in 14 days the disease was to be found in the vascular bundles 
of the youngest scales, and shortly after in those of the older. 
Slightly diseased bulbs are the best parts from which to ob- 
tain the bacteria. In badly diseased plants one runs the dan- 
ger of finding all sorts of things, even Penicillium, in the de- 
