DEVELOPMENT OF DISEASE RESISTANT VARIETIES 

 OF PLANTS. 



By H. S. Jackson, 2neavark, Del. 



Given before the Society, March 14, 190S. 



AVhilc the subject which I have selected may not be of special 

 local interest, I believe it to be of sufficient general interest to merit 

 a discussion before any body of men interested in any branch of 

 agricultural science. In the entire discussion of the development 

 of disease resistant varieties, I may not mention any special crops 

 which are of particular interest to Massachusetts horticulturists, 

 for this phase of plant breeding is not sufficiently developed as yet 

 to enable us to direct the grower how to proceed to obtain results, 

 except with very few crops. The study of the development, by 

 man, of disease resistance in plants is yet in its infancy. I propose 

 to discuss the subject in general, and to give a review of what has 

 already been accomplished by horticulturists and plant breeders 

 in developing plants resistant to specific diseases. 



We must first get a definite idea of what is meant by disease 

 resistance in plants. We must distinguish it from hardiness. 

 Hardiness is a general term. A hardy variety, as generally con- 

 sidered, is merely one that is less susceptible to cutting frosts, 

 drought, or extreme changes in temperature, in short, one that is 

 capable of withstanding adverse cUmatic conditions in a state of 

 health. A disease resistant variety for our present purpose, may 

 be defined as one that shows resistance to the attack of a specific 

 disease due to a specific organism. 



In this age of intensive agriculture, with our advanced and in- 

 creasing knowledge of the principles of culture and fertilization 

 of all sorts of agricultural crops, the question of the health of the 

 plant is recognized as one of paramount importance. We know 

 that under certain conditions, if we give our plants the proper food 



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