18 DISEASES OF ECONOMIC PLANTS 



Cluster cup. — The cup-like sorus in which the spring 

 spores of many rusts are borne. 



Sclerotia. — Small, hard bodies variously colored, but 

 usually black ; masses of compact fungous threads. 



PREVENTION OR CURE OF PLANT DISEASES 



Owing to the comparatively small value of the individual 

 among plants, cure of a plant already sick is seldom at- 

 tempted except in the case of plants of exceptional value. 

 Such value very rarely attaches to annuals or biennials; 

 hence it is only with perennials, valuable vines, bushes, 

 or trees, that cure of the individual is attempted, and here 

 only in a few special cases. 



The burden of the effort of the plant pathologist must 

 be directed toward methods of prevention, which are here 

 worth far more than their proverbial ratio. 



The science of plant pathology, barely antedating 1880, 

 is yet young; its founders in America are still ahve and are 

 still vigorous workers. In comparing this youthful science 

 with its far more aged prototypes, human and veterinary 

 medicine, one is astonished at the progress already made, 

 rather than abashed at the multitude of diseases as yet 

 unconquered. 



Among all classes of crops are diseases, single or many, 

 which have given way to the control of man, many of 

 them diseases of fearful destructiveness, yet which are 

 now completely under the subjugation of the inteUigent 

 educated crop producer. 



The remedies, with one or two exceptions, are entirely 

 the result of patient, scholarly investigation, careful de- 



