EXPERIMENTAL EVOLUTION 



lOS 



viduals measured. The length varied from 8 to i6 

 millimeters, and in the following proportions : 



Millimeters 



Number of beans. 



10 



The beans were then placed 

 in a glass jar divided into 

 nine compartments, all the 

 beans of the same length 

 in the same compartments. 

 When this was done it was 

 found that the beans were 

 so grouped that the tops of 

 the columns in the various 

 compartments followed a 

 curve, known as Quetelet's' 

 curve (Fig. 51). 



This curve may be plotted 

 by erecting vertical lines 

 (ordinates) at intervals of one 

 millimeter on a horizontal 

 line or base, the height of 

 each vertical line being pro- 

 portionate to the number of 

 beans having the length in- 

 dicated in figures at its base. 

 This curve shows the freq- 



108 



12 

 167 



13 

 106 



14 

 33 



15 

 7 



16 



I 



Fig. 51. — Demonstration of 

 Quetelet's law of fluctuating varia- 

 bility in the length of seeds of the 

 . . , common bean (Phaseolus milgaris). 



uency of occurrence of seeds description in the text. (Redrawn 

 dimension from de Vries.) 



of 



any given 



■ So named from its discoverer, Qu6telet (Ket-lay). As de Vries states: 

 "For a more exact demonstration a correction would be necessary, since 

 obviously the larger beans fill up their compartment more than a similar 

 number of small ones." 



