BETTER PLANTS AND ANIMALS 19 



characters, such as the color of the flowers or hair, the markings 

 on the seeds, the shape and size of the leaves and the height 

 of the stems, the horned or polled character in cattle, the gait 

 of the horse (whether the trot or the pace), are the blocks. The 

 blocks that represent single characters are called units, and the 

 characters that behave like units, that is, that cannot be broken 

 up, are called unit characters, or unit factors. Sometimes we 

 find that it takes more than one unit to make a character. 



FIG. 12 b. The modern, improved type of hog 

 Matures rapidly, and is more valuable when mature 



20. MendePs Law and the breeder. Without a knowledge of 

 Mendel's Law, man has developed a great many pure breeds 

 of animals and plants, all within comparatively recent times. An 

 understanding of this law, however, will prove of great value by 

 showing how to produce many more breeds and, especially, how 

 to produce them more quickly. It will help to show the neces- 

 sity of using pure strains when experimenting not to produce 

 new types but to grow a particular kind or quality of plant or 

 animal. It helps to show that what appears to be the character 

 of a hybrid may or may not appear in the next generation. And 



