IMPROVING QUALITIES 



493 



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influenced by her food, health, and care has been modified, 

 whether favorably or unfavorably. In the second case we say 

 that cows of different breed will yield different quantities and 

 grades of milk, though all receive the same food and care. Dif- 

 ferences in feeding affect plants as well as animals. In any season 

 we mav see fields of stunted, 

 backward crops and fields of 

 luxuriant growth. In every city 

 we may see vigorous and alert 

 men and women, as well as 

 shriveled, miserable, and timid 

 men and women. How far can 

 these differences be controlled ? 

 It is impossible to say off- 

 hand in any given case how 

 much of the present condition 

 of a plant or an animal is due 

 to the qualities of its breed or 

 strain and how much is due to 

 the influence of its environment 

 or experience ; but every farmer 

 knows that, besides controlling 

 the conditions under which his 

 plants and animals develop, he 

 must also be careful to select 

 the right kind of stock or seed 

 to begin with. The best of care 

 will not make the ordinary 

 white bean seed develop into a 

 plant bearing seeds as large as 

 the lima bean, nor will extra 



feeding ever make a scrub cow give milk with the high propor- 

 tion of fat that may be obtained from a good Jersey cow. 

 There are, therefore, three Hnes of control: (i) Since there 

 are so many varieties of each species, we must select the best 

 strains of each kind. (2) Having the plants and animals that 



10 11 12 13 14 15 16 17 IS 19 20 21 22 



Fig. 207. Individual variation in 

 the number of repeated parts 



The principal veins on each side of the 

 midrib on a beech leaf vary from lo to 

 22. The number most frequently found 

 is 16. The vertical columns correspond 

 in height to the frequencies with which 

 the various numbers of veins occur. 

 Broken line a, a tree in which the num- 

 ber of veins varied from 13 to 17, leaves 

 with 15 veins being most frequent. 

 Dotted line b, another tree, in which 

 the veins varied from 15 to 20, iS 

 veins being most frequent. Each tree 

 has its individuality, and each leaf has 

 its individuality 



