240 



BACTERIA IN RELATION TO PLANT DISEASES. 



of the root become separated and disorganized. At first in both stem and leaves the bacilli are found 

 only in the vascular bundles. In the leaves the veins are first blackened and then the parenchyma is 

 destroyed. In very recently diseased plants the vascular bundles are only stained locally, while the 

 rest of the tissues are entirely sound. In the first stage of the disease only one side of the stem is 

 black. Later the entire woody tissue becomes black. Sometimes the black stain does not appear 

 until after the stems are cut. The bacteria gradually pass inward from the woody tissue into the 

 pith and outward into the bark. The bark-parenchyma is badly disorganized; cell-sap, starch, chlo- 

 rophyll, nucleus, and the rest of the cell-contents disappear; only the sclerenchymatic cells are very 

 resistant. There is the same disorganization of the parenchymatic parts of the vascular bundles. 

 Sometimes a cork-layer is developed between sound and diseased parts. Small cavities filled with an 

 immense number of bacteria often occur in the stem. The veins of the leaf are often hollowed out 

 by the bacteria. These are often also found swarming, it is said, in the leaf-hairs. When the roots 

 are attacked the first sign is the separation of the bast from the wood. When for any reason the 



attacked plants are not at once destroyed the leaves are dis- 

 torted. The disease causes much damage by its very rapid 

 spread during the rainy season. The spread of the disease is 

 also greatly favored by the high summer temperature. 



F,g. I28.f 



The organism said to cause this disease has been 

 named Bacillus nicotianae by Uyeda. He states that it 

 resembles Bacterium solanacearum, but to the writer it appears to differ very materially 

 in its morphology and cultural characters (if we may assume all these statements to relate 

 to one organism), although the signs of the disease are strikingly like those of the Granville 

 (North Carolina) tobacco wilt. 



Uyeda's description of this organism differs from Bacterium solanacearum, as I have 

 cultivated it, in the following particulars: 



\ ;ai lab and streak cultures of Bacillus nicotianae Uyeda, showing a brown stain in the upper part, 

 the lower portion of each being unstained. (After Uyeda.) 



fPlC illus nicotianae I ryeda, from an agar- plate culture 2 weeks old, showing development of the brown 



stain in and around the colonies. (After Uyeda.) 



