632 IMPROVEMENT OF LIVING THINGS BY MAN 



Verify your figures by having your neighbor take the measurement 

 for you. Do the same thing for him. The instructor will give you an 

 individual number. Hand in your results with your number to one 

 pupil in the class, who will tabulate the figures on the board. 



Make a graph showing individual variation in circumference of the 

 wrist in the members of your class. What are your conclusions? 



Two types of variations occur. Variations in nature appear to 

 be of two types. If we measure the size of a large number of peas 

 or beans, we find that though most of them are of a certain size, 



1 



1 



mmm. 



Cases 3 5 10 20 34 47 54- 44 40 31 -20 3 



The number of markings on a random 313 sunflower seeds was counted. The result of this 

 experiment is recorded in the diagram. 



others will be a little larger or a little smaller, and a very few will 

 be very large or very small. A graph can be made from the results, 

 which shows an even curve, known as Quetelet's (ket'laz) Curve. 

 Such variations are, to a large degree, changes brought about as 

 the result of differences in environment upon the plants produc- 

 ing the seed. Such fluctuating variations would not, therefore, 

 influence the heredity of the next generation, as they have no 

 influence upon the sex cells. On the other hand, such variations 

 may be due to certain combinations of chromosomes and as such 

 are inheritable. This makes the problem very difficult for the scien- 

 tific plant or animal breeder. 



Occasionally, however, sudden changes or discontinuous varia- 

 tions occur. Such was the famous ancon ram which suddenly 



