626 IMPROVEMENT OF LIVING THINGS BY MAN 



hen in a year ; yet the average hen lays less than 100 eggs per year. 

 A few cows of superior breeding in some of the state experiment 

 stations produce as much as 1000 pounds of butter fat each in a 

 year, but the average cow produces little more than 200 pounds 

 a year. A bulletin of the Department of Agriculture says, " Good 

 judges believe that in the entire country one fourth of the cows 

 kept for their milk do not pay for their cost of keeping, and nearly 

 a fourth more fail to yield annual profit." This means that many 

 farmers do not know what their cows are producing. It means that 

 many farmers are poor, through either carelessness or ignorance. 

 The scientific breeding of milk cows would mean millions of dollars 

 in the pockets of the farmer, and an increase in that much-needed 

 commodity, milk. This is only one of the many problems of con- 

 servation that will eventually be solved by our animal breeders. 



Practical Exercise 10. Make a list of all the kinds of domesticated animals 

 and plants in your locality that are useful to man. Indicate on the list all 

 those that you know have been improved by such factors as : selection, budding, 

 grafting, crossing or hybridizing, use of Mendel's laws, etc. After discussion 

 in class make a revised table for your workbook. 



Self-Testing Exercise 



Mendel discovered through experimentation the inheritance of 



(1) (2). Through breeding, some of these (3) 



(4) can be (5). Most new (6) produced 



by Luther Burbank were (7). Certain unit characters are 



(8) over other characters which are (9). If two 



hybrids are mated, their offspring will be (10) per cent re- 

 cessive and (11) per cent dominant in respect to any unit 



character. 



PROBLEM IV. WHAT DETERMINES HEREDITY 



Chromosomes the bearers of heredity. We have learned that 

 a cell contains a nucleus, in which are certain very minute struc- 

 tures known as chromosomes (because they take up color when 

 stained) . When cells divide, each chromosome divides by splitting 

 lengthwise, so that equal amounts of each chromosome are thus 

 carried into the new cells formed from the original cell. These 

 chromosomes are believed to be the structures which contain the 



