THE PRESroEXT's ADDRESS. 37 



of corn is perhaps the most extensive and complex mixture of 

 elementar}- forms exhibited by any cereal crop. It is also found 

 that selection down to a single elementar)- form, followed by rigid 

 pedigree cultures through self-polHnation, results in deterioration 

 to a fixed level, which probably represents the normal level of 

 that form. The explanation seems to lie in the fact that hybrids 

 from nearly related parents are more vigorous than either parent ; 

 and therefore an isolated form that does not enter into a hybrid 

 deteriorates to a certain point. This work suggests, therefore. 

 that while pedigree culture is essential to isolate elementary forms, 

 to obtain what the bacteriologist would call pure cultures, so that 

 they may be recognized and manipulated with intelligence, the 

 ideal second step would be approved combinations of elementary 

 forms, to obtain the increased vigor of a hybrid. In other words, 

 it is first isolation, which means individual selection and pedigree 

 culture, and second recombination. 



This local illustration from our own dominant crop indicates 

 that the method of individual selection, or pedigree culture, is 

 sound in principle, but that its application to any particular crop 

 is a special problem, involving a special technique. 



An illustration or two of the possibilities of pedigree culture 

 may be of interest. The problem of resistance is one of the most 

 important in connection with plant-breeding. For example, it is 

 most desirable to secure resistance to such things as disease and 

 drought, and individual selection has suggested a method of 

 attack. 



The original method of combatting the destructive diseases of 

 culture plants was to determine the parasitic form inducing the 

 disease, learn its hfe history, and discover some means of killing 

 it or of preventing its development. The incidental result of this 

 method has been a gain to science in a greatly increased knowl- 

 edge of the life histories of a most interesting group of organisms. 

 It can hardly be claimed that there has been any gain of equal 

 value to practical plant-breeders. The introduction of individual 

 selection suggested a new method. It was observed that after 

 the most destructive attack of a given disease, certain individuals 

 would remain unattacked ; and it was inferred that one of the 

 characters of such individuals was immunity to this disease. 

 Pedigree culture should perpetuate this character and establish 

 an immune race. A certain measure of success has followed the 

 experimental work undertaken to demonstrate the possibilities, 



