CHAPTER XIV 

 PLANT DISEASES 



Plants are subject to diseases whicli are similar in cause 

 and character to those of the animal, except that the majority of 

 animal diseases are caused by bacteria, while the majority of 

 plant diseases are caused by fungi. 



A healthy plant is one in which all the parts are perform- 

 ing their regular functions ; a plant which is growing and pro- 

 ducing fruit in the regular manner. A disease is any condition 

 which interferes with the regular functions of the plant or 

 causes its death. 



Anything that interferes with the taking of food materials of 

 any kind, with photosynthesis, with the movements of plant 

 fluids, with transpiration, with reproduction or with any other 

 function of the plant is the cause of disease. The disease itself 

 is frequently designated by the name of the causal organism. 



Two Groups of Diseases. — Diseases may be conveniently 

 grouped into organic and environmental: 



Organic (caused by organisms) 



Environmental (caused by surrounding influences) 

 Soil Temperature Smoke 



Moisture Gas Chemical (near factories) 



Some Symptoms of Disease. — A disease may cause (a) dis- 

 colo7"ation of the foliage or other parts of the plant; (&) new or 

 excessive growth ; (c) wilting; {d) unnatural sliedding of parts ; 



139 



