MICBOSCOPIC STUDIES. 157 



that there are depressions of some kind in the walls of these two 

 classes of cells. In small, thin-walled cells of the wood parenchyma 

 there appear to bo no such depressions. 



The bacterial action under these different conditions is according 

 to the structure of the tissue; the thin-walled tissue of the woody 

 parenchyma is completely (Usintegrated and the vessels whicli it 

 surrounds are set free (PI. XIV, figs. 1 and 2). Aj^parently, in tliis 

 case the bacteria have a solvent action on the thin walls, which are 

 b'ttle or not at all ligniiied. In the fundamental tissue when young, 

 disintegration also results from the bacterial action. In such cases 

 swarms of bacteria, adhering in groups which are of the shape of the 

 cells, may commonly be seen with no distinct walls intervening. In 

 older parts of the fundamental tissue when the walls have become 

 somewhat lignified no disintegration takes place; nevertheless, the 

 bacteria gain entrance and cause a disintegration of the contents of 

 the cells. Whether this entrance is gained solely through the pits 

 (or pores) or is effected by some solvent action of the bacteria on 

 the walls is not certain. With the disintegration of the contents of 

 these fundamental tissue cells the walls collapse, and a soft, watery 

 mass results. As the infection becomes farther removed from the 

 growing point where the tissues are harder the softening action is 

 lessened. In the trunk below the heart an actual rot, i. e., a softening 

 to the consistency of a thick liquid, takes place for a distance of half 

 a meter or so below the growing point (in one case 1^ meters). This 

 rot does not affect the outer portion of the tree (cortex), but leaves it 

 firmly bound together by its many wood bundles as a shell surround- 

 ing and containing the soft mass. Toward the lower part of the rot 

 the bundles in the center of the trunk, as w^ell as those at the periphery, 

 remain unaffected, and at the lowest point there is a discolored area 

 which contains no soft rot whatever. It is frequently possible to 

 obtain a bundle of the fibers a foot or more in length which have been 

 freed from the surrounding parenchyma by the rot. Proceeding 

 from the soft tissues upward similar changes are noticed. As the 

 leaves mature the pinnae become very membranous and lose their 

 fleshy condition. The epidermis becomes thicker and hardened to 

 such an extent that it is unaffected by the bacterial rot. The middle 

 tissues may be disintegrated, but the epidermis remams a trans- 

 parent, papery membrane, covering the vascular bundles, or veins. 

 Spots often appear high up in both the mature and young leaves, 

 first as small yellow or brown dots which may gradually spread nito 

 Ions:, brown, water-soaked streaks, or mav be restricted to small dry 

 areas. In the water-soaked streak, which eventually passes down 

 the leaves to the heart, are swarms of bacteria which cause the 

 slimy condition. Fungi also are frequently present. In the small 



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