— 
BLACK ROT OF CRUCIFEROUS PLANTS. 315 
offers a more favorable substratum. Occasionally in cabbage and collards the entire pith 
of a stem disappears (fig. 105) and in turnips it is not uncommon for cavities in the roots 
to occupy a large portion of the interior (fig. 106). 
Although, as stated, parenchyma is destroyed by the wedging apart of its cells, there 
are other ways, 7. ¢., it is not infrequent, as shown in fig. 120 and on cross-section in Vol. I, 
fig. 5, for non-lignified cells surrounding a vessel to be entered and filled by the bacteria 
rather than to be crushed and crowded out of the way by external multiplication. The 
cell-wall appears to be intact as shown in the drawings and clearly no great amount of it 
can be dissolved. It is not easy, therefore, to make out exactly the method of entrance. 
Probably the bacteria enter these particular cells by way of pits, the vessel being first filled 
by the organism which then either dissolves the 
thin separating membrane of the pit or softens 
and ruptures it. 
Harding and Brenner both mention the 
occasional presence in the bacterial cavities of 
granules, which do not stain like bacteria,and 
the origin of which is somewhat doubtful. Hecke 
states that he found such granulesin undestroyed 
vessels just beyond the advancing margin of the 
bacterial mass, as determined by serial sections. 
This substance stained with magdala red but 
did not retain the iron-haematoxylin. The 
material was fixed in a mixture of formalin, 
wood-vinegar and wood-alcohol. Brenner is 
inclined to consider these granules as in the 
nature of bassorin and derived from the decom- 
position of the host-tissues. The writer be- 
lieves some of them to be dead and more or less 
disorganized bacteria, which for this reason do 
not take stains well. Such granules occur in 
great numbers in sugar-cane attacked by Bac- 
terium vascularum. See also Symbiosis, page 111. 
They offer a good subject for further research. 
There are no gaps in the bacterial occupa- 
tion of particular vessels and, consequently, as 
Hecke suggests, movement of the organism in 
the tissues, probably may be assumed to be 
due to growth rather than to self-motility. The 
black stain always follows the bacterial occu- 
pation, rather than precedes it, but the bacteria 
are rarely more than 1 or 2 cm. in advance of the / 
pigmentation, so that to a good degree absence Fig. 113.* 
of brown stain in the vascular bundles may be 
taken to denote absence of the bacteria.t This black or brown stain may be located 
foo M7 m 
*Fic. 113.—Cross-section of small portion of cauliflower-petiole, showing parenchyma to left of fig. 109. Inter- 
cellular spaces occupied by Bacterium campestre. The cells themselves are entirely free. Section stained with carbol 
fuchsin. Slide 118-5. The bacteria entered this tissue by way of one of the bundles in which there is a large cavity. 
_tRussell says ‘‘the causal organism can frequently be isolated at a point 2 or 3 inches in advance of the darkened 
tissue.” (Bull. 65, p. 23.) This I have not been able to verify and am inclined to think it is a mistake. 
Errors may easily occur, since in one of the author’s own examinations of leaves infected on the blade no brown 
stain was detected in a fresh-cut petiole on cross-section, at a certain level, using a good hand-lens, but was plainly 
visible to the naked eye more than 2 inches farther down (away from the point of inoculation) in a few vessels of one 
bundle on mashing the tissues for poured plates, and was then detected on the original cross-section, the surface of 
which had meanwhile become dry and somewhat lighter colored. These browned vessels which contained numerous 
bacteria, were 11 cm. below the place of inoculation, and 6 cm. below the point where the brown stain in the vessels 
was at first supposed tohave entirely disappeared. The poured plates yielded numerous colonies of Bacterium campestre. 
