286 BACTERIA IN RELATION TO PLANT DISEASES. 
vessels. The cells are separated from each other, crushed and dissolved (?) their place 
being taken by the rapidly multiplying bacillus (fig. 62). For an earlier stage of bundle 
infection see vol. 1, fig. 9. In this way cavities arise which by fusion with other cavities 
lead to the honey-combing and more or less complete destruction of this part of the bundle 
and consequently to the interruption of its function, viz., the movement of water. The 
bacteria also pass outward through the lignified tissues (by way apparently of the pits) into 
the large pitted vessels, several to many of which are often filled partly or completely before 
there is any destruction of the phloem or of the general connective tissue of the stem. In 
the end, the bacteria may be found also in the phloem and outside of the bundles in the 
surrounding tissues. For an especially good example of a late stage in which the bacteria 
have passed beyond the limits of the bundle and may be seen occupying the intercellular 
spaces and the interior of parenchyma cells see fig. 81. By this time, however, the stem 
begins to shrivel from loss of water, and the activities of the organism cease, so that the 
phloem and the tissues lying between the bundles, or beyond them toward the periphery of 
the stem, are seldom occupied to any great extent. Frequently pitted vessels at the outer 
angles of the xylem become filled in advance of those 
in the middle. The lignified tissues are not dissolved, 
but the thin non-lignified membrane separating the pits 
on contiguous vessels must be ruptured or dissolved 
by the bacteria—otherwise it is impossible to account 
for their diffusion into the connective tissue of the 
xylem and from one pitted vessel to another. 
It is very easy to demonstrate microscopically 
the presence of the bacteria in the vessels, to cultivate 
them therefrom (when the right methods are used) 
and by means of sections made from pieces embedded 
in paraffin to show all stages in the destruction of cells 
and in the formation of cavities in the bundles. The 
organism occurs also in the green fruits of cucumbers 
and produces therein the same occlusion of vessels and 
breaking down of neighboring cells, with the formation 
Fig. 80.* of small bacterial cavities, as in the stem. The fruit 
finally shrivels and the flesh sometimes has a water- 
soaked look about the bundles, but there is no general disintegration of the parenchymatic 
tissues, z.e., no soft rot. 
Numerous examinations under the microscope have disclosed no tendency of the cells 
of the host-plant to enlarge or divide in the presence of the organism, nor have I detected 
any distortions or suppressions of particular systems of tissues such as we commonly find 
in certain other bacterial diseases. The tissues of the attacked plant seem unable to react, 
except that, as already mentioned, I have observed in the field, in certain squashes attacked 
by this organism, certain proliferations which, rightly or wrongly, I have attributed to its 
presence in the tissues; and also in certain inoculated squash-cotyledons a suggestion of 
cork-formation in the pricked area, and a very slow multiplication of the bacteria in the 
bundles. 
THE PARASITE. 
Bacillus tracheiphilus EFS.—The cause of this disease is a short, straight rod with 
rounded ends (figs. 57 and 82). When growing rapidly in the plant or on culture-media it 
commonly measures 1.2 to.2.5u by 0.5 to 0.7, but it may be longer or shorter or thicker or 
~ *F 1G. 80.—Cross-section of a squash petioles showing 12 vascular bundles occupied and destroyed by Bacillus 
tracheiphilus. ‘Tissue between bundles and toward surface is free from bacteria. Inoculation was made Aug. 10, 1905 
(Colony E, House 4), on blade of leaf by needle-pricks. Froma photomicrograph. Slide 354-3. For detail see fig. 81. 
