conspectus: methods of control 75 



culture. The man who grows one crop year after year on the 

 same soil invites disaster. 



It has jeen found that some cultivated varieties are less sub- 

 ject to disease than others (pear, apple, plum, rose, maize, beans, 

 soy beans, potato, tomato, sugar-cane, banana, cabbage, etc.), and 

 there are also individual variations within the variety. These 

 phenomena lead us to hope that by selection, or hybridization, 

 valuable resistant strains may be originated. Meanwhile the 

 resistant sorts when they are of any value commercially 

 should be substituted for sensitive sorts in localities much 

 subject to the disease. Unfortunately some of the resistant 

 sorts have other less desirable qualities. A vast amount of 

 experimental work must be done in this field before we shall 

 have substantial results, and at least a generation or two will 

 be required to learn even the boundaries of the field. But the 

 problem offered is so enticing, and has such immediately practi- 

 cal bearings on the food-supply of the world, that in the near 

 future we may suppose many pathologists will devote themselves 

 to it, and that long before the whole field is worked over, many 

 useful results will be forthcoming. The labor involved is enor- 

 mous and exacting to discouragement at times, the results 

 come so slowly, so much must be done to be certain of so little, 

 all because the organisms dealt with are very small — how small, 

 we seldom realize ! If the inhabitants of the United States or of 

 Great Britain were reduced to the size of the smaller bacteria 

 the entire population could occupy the surface of a silver dollar 

 or of an English penny — and that too without crowding! 

 O'Gara's happy characterization of the Fire-blight organism, 

 "under the microscope, when magnified 1,000 diameters, its 

 appearance is that of a hyphen '-' " applies equally well to 

 nearly or quite all of the forms described in this book. 



