18 EFFECT OF BLACK EOT OT TURNIPS. 



entirely free from bacteria. In both figures the bacterial contents of 

 vessels have fused. This I take to have occurred through natural 

 openings rather than through openings made by the bacteria, because 

 occasional h' in cross sections of unoccupied bundles I find reticula- 

 tions thinning out and disappearing in the same way. In the lower 

 figure a few of the cell walls have been In-oken and displaced slightly 

 in mounting. 



The upper figure on PL VIII shows an early stage in the destruc- 

 tion of the parenchyma, the intercellular spaces are occupied by the 

 bacteria, but the cells themselves are still free and have not been 

 wedged apart, as in figs, -i and 5, PI. VI. The granular matter in the 

 center of the cells is protoplasmic material. The lower figure shows 

 in cross section a very small vascular bundle. The two reticulated 

 vessels are filled and the bacteria have found their way outside of 

 these into the intercellular spaces which are filled and greatly enlarged, 

 the cells being crowded apart and, in case of one of the lower ones, 

 crushed in. Two or three nonlignified cells are also filled. 



PI. IX shows two stages in the formation of bacterial cavities. In 

 the upper figure there is more or less vagueness in the cell walls, one 

 of which, on the right-hand side, has almost entirely disappeared. This 

 figure shows a single vessel in the center (comparable to fig. 1, PI. V). 

 The surrounding cells which are so fully occupied by the bacteria are 

 nonlignified wood cells of the fleshy root. In the lower figure there 

 has been a greater softening of tissue and a considerable cavity is in 

 process of formation. Here in the center (from right to left) are at 

 least four vessels, and there is probably a fifth vessel just above the 

 cell marked X. The reader's attention is called particularly to the 

 vagueness of the cell walls and to the open cavity which is shown in 

 the lower middle part and the left-hand part. The whole forms a very 

 instructive and typical picture of the way in which cavities are brought 

 about by the mechanical and solvent action of this organism. The 

 tissue for a long distance around both of these foci is sound and entirely 

 free from bacteria, and, as in the other cases, the bacteria could have 

 entered these bundles only as a result of the leaf inoculations already 

 described. 



On PI. Xare shown two figures illustrating a further advance in the 

 destruction of the parenchyma of the root and the formation of bac- 

 terial pockets. The cells are separated from each other by masses 

 of bacteria, are crushed in, and are slowly dissolving, their walls 

 becominp- vaguer and vaguer until at the middle of the cavity they 

 can not be seen at all. Fme examples of this gradual destruction of 

 the cell walls are to be seen in both of these tigures. The reader's 

 attention is called in particular to the right-hand side of the upper 

 figure, showing bacterial occupation of the intercellular spaces which 

 usually precedes the formation of an open cavity. In the upper part 

 of the upper figure, in the last one of the second row of cells at the 



