DESTRUCTION OF TISSUES. 77 



small size and the great liability to misinterpretation, i. e., in sections there is often an 

 opportunity for differences in judgment as to whether a particular bacterium actually lies 

 in or over a wall; has really passed part way through the wall by a solvent action of its own; 

 or has only been dragged or flooded a little way out of its original position during the prepa- 

 ration of the slide. Potter took the former view and figured a case of a single bacterium 

 halfway through a cell-wall, but I have yet tomeeta plant pathologist who has been con- 

 vinced by his figure. Probably by mass-action the bacteria push or dissolve their way 

 through pits or similar very thin places in the wall, but the demonstration is hedged about 

 with difficulties. Some of them are at the limit of vision, and might perhaps enter through 

 openings too small to be seen, i. c, of a diameter less than a wave-length of light. That 

 they do enter in some way is certain. The most striking example, perhaps, is the voluminous 

 intracellular occupation in the root-nodules of Leguminosae. Here the cells are often 

 crowded with bacteria with no visible opening for entrance. They seem to enter by mass- 

 action, the bacteria being compacted into strands. Often there is a trumpet-like expansion 

 where the strand touches the cell- wall. The writer has seen what appears to him to be a 

 similar dense occupation of unruptured cells in the bark of the pear attacked by Bacillus 

 amylovorus. The particular tissue which shows this to best advantage is the pitted collen- 

 chyma toward the outer part of the bark. In a few cases it has seemed as if bacteria could 

 actually be traced from one cell into another across a narrow pit, but of the absolute correct- 

 ness of this view I have not yet fully satisfied myself. Moreover, unless I am mistaken in 

 my interpretation Bad. tumefaciens occurs commonlyin the closed cells of the rapidly multi- 

 plying parenchyma of crown-galls. In crown-gall we do not know, except in case of the 

 initial wound, that there is ever any penetration of cell-walls, rather, as already described, 

 it would seem that the bacteria are carried over from mother cell to daughter cells at the 

 time of cell-division. Other examples of the entrance of bacteria into closed cells are shown 

 in figs. 8 1 and 120. 



In quite a good many diseases large cavities arise in the interior of the plant, the cells 

 being crushed and crowded aside, the walls becoming more and more indistinct until they do 

 not any longer yield the cellulose reaction, and in some cases they seem to have nearly or 

 quite reached the stage of dissolution and actual disappearance, as in black rot of turnips 

 and wilt of cucumbers. Whether they ever quite disappear is a subject for future inquiry. 

 None of the bacteria I have tried have any solvent action on filter paper or cotton fibers, 

 but this, of course, is beside the main issue, since there are several kinds of cellulose, some 

 easier of solution than others. 



Nothing is known by the writer respecting the solvent action of bacteria on lignin and 

 cork. Janse asserts that the lignin of Erythrina roots is dissolved by bacteria. The writer 

 tried in vain to obtain material of the diseased Erythrina roots for study. 



The early history of the solvent action of bacteria on cell-walls, so far as it relates to 

 plant pathology rather than to chemistry, is summed up in the writings of Davaine and 

 Van Tieghem. 



As early as 1866, Davaine succeeded in rotting certain plants by inoculating them with 

 infusions containing bacteria. These experiments antedate those of Van Tieghem by more 

 than a decade. He called his organisms Bacterium putrcdinis. 



In 1879 Van Tieghem detailed the success he had had in rotting land plants with his 

 Amylobactcr. Aquatics resisted. The meristematic tissue was that most easily attacked. 

 The following are two pertinent paragraphs: 



Are the membranes of vegetable cells all attacked by A mylobacter indifferently ? By no means. 

 I know only one state in which all the cells of all plants are equally dissolved by it, no matter how 

 thick they may be, viz., the embryonic state. As soon as the plant has specialized and solidified 

 its tissues by development, profound differences are noticeable [p. 27]. 



But it is by no means the same in submerged phanerogamous aquatics. Here the cellulose of 

 all the elements of the stem and of the leaves resists Amylobactcr, and for these kinds of plants 

 resistance is a necessity of existence [p. 28]. 



