CHAPTEE I 



THE NATURE AND SYMPTOMS OF DISEASES 



IT has been well said that " a plant is in health when 

 all its organs or parts are doing their proper work, and 

 the processes of growth and reproduction are going 

 forward in the natural and regular manner." It must 

 then be equally true that when any of the organs and 

 parts of a plant are not doing their proper work, and 

 when either the growth or reproduction are not going 

 forward in the natural and regular manner, the plant 

 is diseased, regardless of the cause or causes of its 

 abnormal condition. 



It therefore becomes necessary to distinguish 

 between the cause of a disease of a plant and the 

 diseased condition of the plant. Insects which eat 

 parts of a plant or suck the juices are not diseases, but 

 they may interfere with the performance of the normal 

 functions of the plant and cause a weakened or un- 

 healthy condition. This weakened condition may also 

 so reduce the vitality of the plant as to make it 

 susceptible to organisms of disease. 



Fungi, bacteria, and flowering plants growing upon 

 or within the tissues of a plant are not diseases, but 

 frequently the cause of some of our most serious 

 diseases. Likewise the character of the soil, the amount 

 and distribution of moisture, and the climatic con- 

 ditions may be the causes of severe and destructive 

 diseases. 



1 Earle, F. S., " Health and Disease in Plant?." Journal New York Botanical 

 Garden, vol. iii., No. 35, pp. 195-202. 



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