CHAPTER XLIV 



IMPROVING QUALITIES IN PLANTS AND ANIMALS 



Questions. 1. What qualities in various plants are important in hu- 

 man affairs ? 2. What are the qualities in animals that are important to 

 us ? 3. Are the domesticated plants and animals of today the same as 

 those of ancient times ? 4. How do domesticated animals and plants 

 differ from wild species ? Where did they come from ? 5. How can 

 plants be improved or otherwise changed ? 6. How can animals be im- 

 proved or changed ? 7. Will large plants produce larger seeds than small 

 ones of the same kind ? 8. Will large seeds produce larger plants than 

 small ones of the same kind ? 9. Would more food change a pony into 

 a full-sized horse ? 



362. No two alike. In some respects all the members of a 

 species are alike. That is why we call all dogs "dog," and all 

 apple trees "apple tree." But in some respects every individual 

 is unique. If you should get the tips of your fingers inky and 

 place them on a sheet of paper, you would make a set of marks 

 that could not be exactly duplicated by anyone else. All species 

 of plants and animals present this fact of individual variation. 

 There is variation in size and in proportion (Fig. 206), in color- 

 ing and in shading, in the number of duplicated parts, like the 

 ribs of a leaf or the hairs on a given surface (Fig. 207), and in 

 physiological properties, like the yield of milk, the proportion 

 of sugar, the amount of sleep people need, relative immunity 

 to infection, and so on (Figs. 208 and 209). 



363. Causes of variation. If a cow is undernourished, she will 

 not yield as much milk as she might. This accounts for much 

 of the difference between one farmer's cows and his neighbor's 

 cows. On the other hand, in a herd of cows that receive the 

 same care and feeding from birth, some will produce more milk 

 than others. In the first case we say that the yield of the cow, 



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