342 GENERAL PLANT PATHOLOGY 



Knowing the specific fungal organism, a great stride has been made 

 toward a comprehensive knowledge of the disease. 



The plant pathologist, who would be successful in his profession, 

 must be acquainted with the normal, or healthy, conditions of plants, 

 or how can he study the unhealthy states? Any departure from the 

 healthy state is indicated by a certain behavior of the plant, or reac- 

 tion to the causes of disease and certain p)eculiarities of structure, form 

 and color are also manifested. An investigation of these character- 

 istics of disease concerns symptomatology. The most common symp- 

 toms of plant diseases may be classified according to the outline pre- 

 sented by Heald in Bulletin 135 of the University of Texas, Nov. 15, 

 1909, entitled "Symptoms of Diseases in Plants." 



1. Dbcoloration or change of color from the normal. 



(a) Pallor. Yellowish or white instead of the normal green. 



(b) Colored spots or areas on leaves or stems. 

 Whitish or gray: mildews; white rusts, etc. 

 Yellow: many leaf spots. 



Red or orange: rusts, leaf sf»ots, etc. 

 Brown: many leaf spots. 

 Black: black rust, tar spots, etc. 

 Variegated: leaf spwts, etc. 



2. Shot-hole: perforation of leaves. 



3. Wilting: " damping-off," "wilt,!' etc. 



4. Necrosis: death of parts, as leaves, twigs, stems, etc. 



5. Reduction in size: dwarfing or atrophy. 



6. Increase in size: hypertrophy. 



7. Replacement of organs by a new structure. 



8. Mummification. 



9. Change of position. 

 ID. Destruction of organs. 



II. Excrescences and malformations. 



Galls: pustules, tumors, corky outgrowths, crown galls, etc. 

 Cankers: malformations in the bark generally resulting in an open 



wound. 

 Pimks or conchs and other fruits of fleshy fungi. 

 Witches' brooms. 

 Rosettes and hairy root. 



