CHAPTER IX 

 DISEASES OF WHEAT 



Introductory. Studies in plant pathology of any great prac- 

 tical bearing or importance are decidedly and characteristically 

 modern and recent. In 1885 there were three institutions in 

 the United States besides the department of agriculture which 

 were making systematic efforts in experimental work with 

 plant diseases, and in disseminating such knowledge as then 

 existed in these lines. Ten years later over one hundred special 

 investigators were devoting their time to this work, and 50 

 colleges and stations were endeavoring to solve its practical 

 problems. The science of plant pathology has had its highest 

 appreciation during the last decade, for some of the outlying 

 problems have been solved, a working foundation has been laid 

 from the facts that were acquired, and a body of institutions 

 with specialists and resources has been developed for scientifi- 

 cally prosecuting the work. 



The Classification here followed is practical and inclusive, 

 rather than scientific and exclusive. There is nothing patho- 

 logical in the sudden destruction of a field of wheat by floods 

 or locusts, but excessive moisture or the presence of a parasite 

 may each bring about diseased conditions, and every gradation 

 of phenomena between these two types must be considered. 



Sources of Injury and Weakness are of three kinds: (1) 

 Unfavorable inanimate environment; (2) unfavorable animate 

 environment; and (3) poor seed wheat. When these three sets 

 of factors occur in combination, as they frequently do, their 

 relations and inter-relations are so intimate and intricate as to 

 be inseparable. Only in a general way can they be individually 

 studied. 



WEATHER AND SOIL INFLUENCES 



Unfavorable Inanimate Environment. DROUGHT; HAIL, WIND 

 AND RAIN STORMS; FLOODS; FIRE. The operation of these de- 

 structive influences needs no further elucidation than a mere 



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