486 



DISEASES OF ECONOMIC PLANTS 



FUNGI AND BACTERIA 



Fungi and bacteria are devoid of chlorophyll, therefore they 

 cannot utilize the carbon of the air and are dependent, for their 

 carbon supply, upon this element as elaborated by some other 

 organism. When they take this food (often other nutrients as 

 well) from living plants or animals, they become parasites, and if 



Fig. 207. — Apple cells invaded by the mycelium of Volutella. 

 OrigiDal. 



their thievery becomes considerable, a condition of disease is pro- 

 duced. By growing in the plant body they may also derange the 

 vital functions in many ways. The fungous plant pathogens 

 usually consist of a threadlike body (the mycelium. Fig. 207), 

 which grows within or upon the plant. Masses of mycelial 

 threads may be large enough to be visible to the naked eye. 



