302 THE PARASITIC DISEASES OF PLANTS. 



tissues to become much softened, thus producing the soft rots, or they 

 may fail to cause this softening but injure them in other ways, so that 

 the plant does not rot but becomes filled with bacteria and the tissues 

 are much injured. These are sometimes called Bacterioses. 3. 

 The Tumor Diseases. In these cases the bacteria cause the forma- 

 tion of unusual growths, tubercles, or tumors, on the various parts of 

 the plants. 



The Wilts. The black rot of cabbage belongs to this class and 

 is really not a "rot," but a wilt. In addition, three others will be 

 briefly described. 



Brown Rot of Potato, Egg Plant and Tomato (B. solanacearum) . 

 Although frequently called a rot, this disease is really a wilt. It is a 

 widely distributed disease of the potato, especially in the northern 

 part of United States and Canada. The leaves of the attacked plant 

 first wilt and shrivel and then the stem turns brown or black. The 

 affection extends down the vascular bundles and may reach the 

 tuber. In this it spreads through the vascular bundles, causing in 

 time a destruction of the potato that has given to it the name of 

 brown rot. The bundles are found to be filled with bacteria in 

 great numbers, that destroy the cell walls, finally causing the com- 

 plete disintegration of these tissues. The isolation of the bacterium 

 is easy and inoculation experiments show that it is capable of pro- 

 ducing the same disease in various members of the potato family. 

 The bacterium appears to be carried from plant to plant by insects, 

 and the potato beetle is an important agent in its distribution. 



The term potato rot is applied to any form of disease that is 

 followed by the rotting of the potato. There are several different 

 parasites that produce this phenomenon, some of them belonging 

 to the higher fungoid types. It is thought that this bacterial disease 

 is the cause of the larger part of the rots in our Northern States. A 

 second bacterial rot of the potato is caused by a bacterium named 

 B. solanisaprus (Har.). It is also a wilt rather than a rot, as we 

 have used the terms, although after it affects the tuber itself it pro- 

 duces a general decay of the tissues. It is common in Canada, 

 where it was first described. A third bacterial potato rot is caused 

 by B. atrosepticus (VanHall). 



