OTHER BACTERIAL DISEASES OF PLANTS 325 
plants, all of the family Crucifere. So, as with the other diseases, 
the same parasite may attack several hosts. 
Classification of Bacterial Diseases.—Plant diseases are less 
clearly defined and classified than animal diseases. Popular 
names have been applied to them without careful discrimination 
till the popular names have ceased to have any sharp meaning. 
The bacterial diseases may, however, be fairly well divided into 
three types, distinguished by the kind of effect they have upon 
the host. These are: (1) The Wilis. In these the bacteria attack 
chiefly the vascular bundles, either destroying their cells or clog- 
ging them. This shuts off the ordinary water-supply to the 
plants and causes them to wilt and wither. (2) The Bacterioses 
and Rots. In these diseases the bacteria invade the tissues 
generally, not being confined to the bundles, and destroy the 
plant cells at once. They may cause the 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 Tomaio (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 
