18 



PLANT BREEDING. 



any chosen characteristic, there are a few which excel, and also a few 

 whicli are considerably below, the medium in that quality. 



This has been illustrated by Quetelet in taking the heights of many 

 men chosen from the same race and reared in the same country. If a 



Fi(i. 1.— Graphic i xprcssion of Quetelet's law. 



thousand men are arranged in a row in order of height, it will be 

 found (1) -that the man in the middle represents the average height of 

 all the men; (2) that a line drawn over their heads will deviate from 

 the horizontal but slightly throughout nearly its entire lengtli, falling 

 slightly toward the end where the shorter men stand; (3) that near 



6 

 5 

 4 

 3 



% Plant Nrfs. 



o 

 Fig 3.— Yields, In grams, of 80 Power's Fife wheat plants grown in field-croi) nnrsery, arranged 

 in order as numbered. Each i.erpendicnUir line represents an individual plant, and the yield 

 in grams is indicated by the horizontal lines numbered on the left, the length of hne below the 

 zigzag line representing the yield. • 



the upper end the line will rapidly curve upward, and that near the 

 lower end the line will rapidly curve downward. Figure 1 is the 

 graphic expression of these facts. The men range from four feet and 

 a fraction to nearly seven feet in height, tin- average being about 5f 

 feet. 



t 



Is Plant No's. 



Fig. a —Yields, in grams, of 80 Power's Fife plants (the same as shown in fig. 2 1 . arranged in order 



of yield. 



The writer has applied this form of gi-aphic expi-ession to charac- 

 teristics of wheat and other plants where the measures of qualities 

 may be expressed in numbers, which in turn may be represented by 

 the heights of vertical lines. In Iiluiv 2 is shown the yields of 80 



