310 BACTERIA IN RELATION TO PLANT DISEASES. 
and thence into the stem where, in turn, the vessels of the stem are occluded and browned. 
Subsequently if the tissues are soft enough the organism passes up and down the stem and 
out into other leaves, always by way of the vascular system. The rapidity of movement in 
stems depends on their texture. In hard woody stems the bacteria move with extreme 
slowness or are entirely hemmed in; in soft juicy stems progress resembles that in the 
petiole. In leaves which are infected from the stem (fig. 98), the entire leaf-blade may be 
attacked almost at once and in that case may show signs of wilting. The writer has fre- 
quently seen cabbage leaves become flabby, unjoint and fall off while the bacteria were still 
confined to the petiole, such leaves having been infected by way of the leaf-traces as the 
result of stem-inoculations. In these cases so many leaf-traces were involved that the leaf 
was unable to obtain the necessary water-supply. More often some of the leaf-traces are 
not involved and the leaf manages to function more or less imperfectly for a considerable 
time. In such a leaf a part of the veins in the 
leaf-blade are always blackened considerably in 
advance of the remainder and wilting may not 
occur. The writer tried passing 1 per cent eosine 
water up such petioles by transferring them to 
the red fluid after cutting them under water. In 
many cases the eosine only passed up the unob- 
structed vessels, but whether failure to pass up 
the bacterially occluded vessels was due simply 
to the occlusion, or must be ascribed in part to 
the destruction of the vessel-walls by the bacteria, 
was not determined. 
Whether the first signs on the expanded 
portion of such leaves are basal or terminal, or on 
one side or the other of the blade, depends en- 
tirely on which leaf-traces are entered first, dif- 
ferent ones ramifying to different parts of the 
leaf (Smith, Hecke). In the end, such leaves are 
so badly affected that they unjoint and fall from 
the stem, without, however, any signs of soft rot. 
It is a slow dry-rot even in turnip-roots. When 
soft rot or extensive sloughing of the parenchyma 
intervenes, especially if it begins at the surface, 
we may at once suspect complications due to the 
presence of other organisms (see the soft rots). 
When inoculations are made on the midrib of a 
leaf, Brenner states that the bacteria pass up- 
ward faster than downward. The writer recorded the same fact for inoculated cabbages in 
1897, and observed it again particularly in 1906. The writer has frequently observed the 
inoculated side of the plant to become diseased almost to the exclusion of the other side, 
but has observed nothing suggestive of the rapid transportation of the bacteria for long 
distances in a liquid moving stream such as we sometimes conceive to be present in the 
vessels of a plant. Ina plant inoculated on the stem under the fourth leaf Brenner observed 
the fourth, fifth, and seventh leaves, which were on the inoculated side of the stem, to 
contract the disease sooner than the sixth leaf, which was on the opposite side of the stem 
(see cucumber wilt, p. 219). Brenner endeavored to force stained bacteria up cabbage- 
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*F 1c. 108.—Small portion cf acabbage-leaf near margin, showing how black venation due to Bacterium campestre 
is frequently restricted for a time to angular areas formed by larger veins. This infection may have started from an 
insect bite at a, or may have run in from a group of water-pores; at b, is another insect bite. Specimen from a cabbage 
field in Western New York. Drawn froma photograph. About natural size. 
