PRINCIPLES OF HORSE BREEDING 



261 



Crossing. — Because of the strong tendency to produce 

 variation, crossing is seldom employed as a system of 

 breeding horses. The crossing of breeds results in the 

 production of nondescript offspring, that lack in efficiency 

 and that fail to command a remunerative price when 

 placed on the market. Attention is directed to crossing 

 as a system of breeding, largely because.it is the method 

 employed in breeding mules, the offspring of a jack and 

 a mare; as well as the hinny, the offspring of a jennet 

 and a stallion. It is interesting to note that the mule 

 more nearly resembles the jack, while the hinny resem- 

 bles the stallion. This 

 has given rise to the 

 statement that the off- 

 spring resembles the 

 sire in external char- 

 acters and the dam in 

 the internal characters. 



Gregor Mendel 

 crossed a number of 

 plants and studied the 

 inheritance of contrast- 

 ing characters in the 

 hybrids. By pairing 

 certain characters, as 

 color, form, and the 

 like, he discovered that 

 hybrid parents produced offspring of which one-half were 

 again hybrids; while one-quarter were pure to each of 

 the original parent forms. This is called "Mendel's Law 

 of Hybrids," and through its application plant breeders 

 are able to transfer certain characters from one group of 

 plants to another. This promises a great field of useful- 

 ness among plants and the law is receiving universal at- 

 tention, although it is little used by horse breeders. 



Line-breeding. — When animals of a single line of 

 descent are mated the system is called line-breeding. It 



Fio. 130. — American Saddle Mare 



