IMPROVEMENT OF PLANTS AND ANIMALS 247 



particular. The law in organic life by which offspring 

 have some difference or variation from the parents is 

 called the law of variation. By methods of breeding 

 that cause variations to become permanent characters, 

 we have obtained beef cattle and dairy cattle, mutton 

 sheep and wool sheep, draft horses and race horses, 

 and many other breeds, each of which possesses some 

 particular advantage. 



Environment largely determines the character of 

 plants and animals. For example, on the lower slopes 

 of high mountains, where the climate and soil are fa- 

 vorable, the evergreen trees are large .and of good 

 form, while at the upper limit of trees near the snow 

 line the evergreens, although of the same species as 

 those of the lower forests, are only two or three feet 

 high and bushy in form. At this high elevation the 

 hard conditions of life have stunted the trees. The 

 small Shetland ponies are the result of the severe cli- 

 matic conditions of their native home, the Shetland 

 Islands, of the far north. By making a better environ- 

 ment for the domesticated animals and plants man has 

 greatly improved them. Shelter from severe weather, 

 and the proper amount and kind of food have made 

 the farm animals more serviceable to man than their 

 wild ancestors. By improving the soil man has im- 

 proved the character of cultivated plants. 



Crossbreeding is another method of improving 

 plants and animals. For example, one variety of 

 corn may have one very useful character, and another 



