PRACTICAL PROBLEMS 



The reciprocal cross. Strange as it may at first appear, the 

 two possible crosses by interchange of the sexes often, though 

 not always, differ substantially. It is said that the common 

 mule more nearly resembles the ass, and the hinny the horse. 

 Other instances have been noted, and the point has been urged 

 that reciprocal crosses are in general dissimilar. It is the 

 writer's opinion that the rule applies only to those particular 

 characters in which the one parent (either male or female) is 

 prepotent over the other because of sex. However, statistical 

 evidence on reciprocal crosses is almost totally lacking. 



The whole subject of hybridization seems at present to 

 promise little of interest to animal breeders beyond the produc- 

 tion of the common mule, but if we may place a shrewd guess, 

 it will yet be found a fruitful source of new varieties in certain 

 races of plants, in which propagation is so easily effected by 

 budding, grafting, or other form of asexual multiplication, thus 

 avoiding the effects of Mendel's law in a way quite impossible 

 with animals. 



SECTION IV LINE BREEDING 



By " line breeding " is meant the restriction of selection and 

 mating to the individuals of a single line of descent. The pur- 

 pose of this system of breeding is real breed improvement, 

 to get the best that can be gotten out of the race, and better 

 than ever before if possible. 



Experience has shown that if the purpose be breed improve- 

 ment, or even herd improvement carried to its limits, it is not 

 enough to confine selection to the limits of the breed. All 

 breeds are exceedingly variable, and real results aiming at any- 

 thing more than mere multiplication can follow only closely 

 drawn lines within the breed, breeding in line, or line breeding. 



Line breeding excludes everything outside the approved and 

 chosen line of breeding. It not only combines animals very 

 similar in their characters, but it narrows the pedigree to few 

 and closely related lines of descent. This ''purifies" the pedi- 

 gree rapidly and gives the ancestry the largest possible oppor- 

 tunity. The system is eminently conservative. It discourages 



