SYSTEMS OF BREEDING 627 



exceedingly valuable races could be established in this way, 

 especially on restricted areas and more particularly with field 

 crops. 



But in actual practice the breeder following this method 

 among animals succeeds in getting together a confused jumble, 

 out of which nothing of note can be established. It is the 

 practice followed by primitive races and by careless farmers, 

 and as soon as some attention is paid to strains, to families, 

 and to blood lines, it passes at once into some one of the other 

 forms of breeding already discussed. 



In plant breeding the principle operates differently. Here 

 numbers may be employed so extensively that after having 

 chosen the stock we can literally hunt through thousands for 

 the thing we want. This when found is, strictly speaking, a 

 mutant, and having found it the plant breeder may proceed at 

 once to multiply it by cuttings or to breed it pure, possibly by 

 inbreeding, certainly with as little crossing as possible. This is 

 the system followed by Luther Burbank, and by plant breeders 

 generally who are looking for new things, though it is often 

 combined with crossing. 



Neither in animal nor in plant breeding, however, are we to 

 expect much success except by regarding ancestral lines and 

 living and working in full realization that the law of ancestral 

 heredity is a fact. 



Summary. The system of breeding to be followed depends 

 upon the purpose to be accomplished. Grading is the practical 

 method of improving common stock and of quickly and cheaply 

 getting acquainted with the essential characters of a breed. 



If the purpose is breed improvement through the perfection 

 of family lines, then line breeding and even inbreeding will be 

 the systems found most effective. 



If new types, new strains, and new creations generally are 

 sought, two courses are open, either to watch for accidental 

 mutations, or to hasten their appearance by crossing, a form 

 of breeding that produces individuals which are good, but which, 

 under the common law of ancestral heredity, are too bad mix- 

 tures to produce a uniform type, and under Mendel's law are too 

 unstable to produce a constant type of any kind. The system 



