106 HEREDITY AND EVOLUTION IN PLANTS 



between the two limits or extremes, and is therefore often 

 referred to as a curve of frequency. It should be noted 

 that, in the case illustrated, the greatest frequency (in- 

 dicated by the highest point of the curve) very nearly 

 coincides with the average dimension; in other words, the 

 more any given character departs from the average for that 

 character, the less frequent is its occurrence. 



In another experiment, ears of corn, harvested from 

 the same crop, were measured and found to vary in length 



FIG. 52. Curve of fluctuating variation (Qu6telet's curve), formed by 

 arranging 82 ears of corn in ten piles, according to the length of the ears. 

 The extremes were 4.5 and 9 inches. The ears were taken from unselected 

 material from a field of corn. (After Blakeslee.) 



from 4^ inches to 9 inches; the largest number of ears 

 (20) were 7 inches long. The greater the departure from 

 this length, in either direction, the fewer the individuals; 

 for the lengths 4 inches and 9 inches the frequency was 

 zero. When the ears were arranged in piles according 

 to their length, the tops of the piles indicated the curve 

 of frequency (Fig. 52). 



The curve of frequency indicates the quantitative dis- 

 tribution of any character or quality when its occurrence 

 is dependent largely upon chance. This is strikingly 



