314 BACTERIA IN RELATION TO PLANT DISEASES. 
In experiments with Bacterium campestre on kohlrabi Hecke found that when the plants 
were kept excessively moist under bell-jars some parts of the leaf-edge became water- 
logged (glossy and darker colored) from an excess of water. These parts subsequently 
died but the plants did not contract the disease from water-pores situated in such suffocated 
areas. Consult chapter on Angular Leaf-spot of Cotton for similar observations by the 
writer. The leaves of maize seedlings also frequently become water-logged without con- 
tracting Stewart’s disease. 
Query.—Why do the bacteria multiply so abundantly in the ence 
MORBID ANATOMY. 
This organism causes no hyperplasias. After it has gained an entrance, which must 
be ordinarily through parenchymatic tissues (epithem, etc.) the parasite is confined for 
some time pretty closely, although not exclusively, to the vascular system and even to 
particular leaf-traces or bundles especially to the spiral and reticulated vessels which are 
very often filled with incalculable numbers of this organism (figs. 111, 112). When such a 
state of occlusion exists, especially in juicy parts, the walls of the vessels are destroyed 
in places (dissolved?) and the organism finds its way into the surrounding parenchyma, 
but never or almost never to the surface of the plant. 
Progress through the parenchyma is slow, apparently 
on account of its acidity. Often the intercellular 
spaces are first occupied (figs. 113, 114); the middle 
lamella is then dissolved (figs. 115, 116) and the 
elements are separated and squeezed into all sorts of 
shapes by the multiplication of the bacteria (fig. 117). 
Subsequently the wall proper of the cell becomes 
thinner and vaguer and finally seems to disappear 
altogether. There may be some doubt, however, on 
the latter point, 7. e., as to the final complete solution 
and disappearance of the cellulose. The dark band 
at the bottom of fig. 110 is probably formed of com- 
pacted cell walls crowded out of the cavity. Similar 
cell-walls crowded out of the center of the cavity may 
be seen in fig.117 as white lines. Lignified tissues are 
not dissolved although Brenner states that they are. 
This statement probably rests on some misinterpre- 
tation. The spiral threads and other distinctly lignified portions of the bundle persist. It 
is the destruction of the surrounding non-lignified tissues which gives rise to the large cavi- 
ties in turnips and other susceptible tissues. 
The formation of cavities by this organism is very common in a number of host-plants 
(figs. 109, 117, 118 and Vol. I, figs. 6 and 7) and all stages of the separation and destruction 
of the cells may be studied to good advantage in turnip-roots and cabbage-leaves or cauli- 
flower-leaves, especially the petioles. The occlusion of the vessels and the formation of 
cavities may also be made out very satisfactorily in kohlrabi and rape (figs. 107,119). These 
cavities always begin in the vascular bundles and are occupied by the bacteria in incalcu- 
lable numbers, scarcely anything like it being observed in the animal kingdom. Small 
parenchyma-cavities sometimes appear around the smaller blackened veins in leaf-blades, 
but more conspicuous ones are to be found in the fleshy midrib and petiole. As a whole the 
parenchyma of the leaf-biade appears to be too dry or too acid for this organism. The pith 
*Fic. 112.—Bacterium campestre occupying a reticulated vessel in a turnip-root as result of a pure culture inocula- 
tion on blades of leaf. Same vessel as shown in fig.120 but a little farther down. Drawn from a photomicrograph. 
_X 500. 
