265 PLANT DISEASES 



Smce the plants known as bacteria have at least 

 similar methods of life and cause many diseases not 

 only in animals but in plants, some botanists include 

 them within the group of the fungi. These bacteria are 

 among the chief agents of the diseases of man, such as 

 tuberculosis, diphtheria, cholera, and many others. 



Since the fungi are plants, it will be well to compare 

 them with plants with which one is ordinarily acquainted, 

 namely, the common flowering plants. The flowering 

 plants may be called independent plants because they 

 are able to manufacture food from the elements of the 

 soil, and from air by the use of sunlight working on the 

 green material, or chlorophyll. The most important and 

 conspicuous difference, at least from our standpoint, 

 between the fungi and the independent green plants, 

 lies in the fact that the fungi do not possess any chloro- 

 phyll. This factor has a very deep meaning, namely, 

 that the fungi are dependent, not independent, plants. 

 In other words, they cannot manufacture their own food 

 as the green plant does, but must derive at least a part 

 of their nutrition from some other plant or animal. 



There are two ways, in general, in which the fungi 

 and bacteria may derive that part of their nutrition 

 which they are required to get from preceding plants 

 or animals. These two methods of sustaining life 

 form the basis of a division into two classes. The 

 first class comprises the parasites, which live directly on 

 growing plants and derive their nutrition from these 

 living plants. Well-known examples of this are smuts 

 of corn and other cereals, and the bacteria which cause 

 the diseases of man mentioned above. The second 

 class of fungi consists of those which do not live on other 

 \iving things, but which get their nutrition from the 



