THE BACTERIAL DISEASES OF PLANTS 321 
Squash.—Anthracnose, Colleioirichum lagenarium; black mold, 
Rhizopus nigricans; downy mildew, Plasmopora cubensis. 
Strawberry.—Fruit rot, Botrytis sp., leaf blotch, Ascochvta 
Fragarie@; leaf spot, Mycospherella Fragarie. 
Tobacco.— Root rot, Thielavia basicola. 
The above list contains only a few of the very large number of 
known fungous diseases of plants, but will serve the purpose of 
showing their variety. ‘The fungi that produce these diseases are 
by no means closely related to each other. The fungi are divided 
into many classes and the disease-producing parasites are dis- 
tributed among them all. For these distinctions, however, the 
student must be referred to books upon botany. 
THE BACTERIAL DISEASES OF PLANTS 
Only within recent years has it been appreciated that bacteria 
are important agents in producing plant diseases. Even after 
their agency in causing diseases in animals had been fully recog- 
nized it was denied that they could produce troubles of this sort 
in plants. Up to very recent date, it was claimed that it was an 
impossibility for bacteria to penetrate plant tissue so as to produce 
trouble. Plant cells are provided with hard cell walls of cellulose 
and wood, which protect the living protoplasm within; and, since 
these cells form the bulk of the plant and are adherent to each 
other, it was difficult to see how bacteria could penetrate into the 
plant at all. The mycelium of the higher fungi can do this readily 
since it can thrust itself between the cells, and thus grow easily 
within the solid tissues; but it seemed impossible to believe that 
bacteria could penetrate the hard tissues. Within recent years, 
however, it has been demonstrated that this is possible and the 
last ten years have disclosed many bacterial diseases of plants, 
until to-day we know of more bacterial diseases of plants than of 
animals. 
The Black Rot of Cabbage (Pseudomonas campestris) —An 
illustration will best show the general course of such a disease and 
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