20 



PLANT BREEDING. 



nursery; there is an aluKn-iiially large "infant niortality" and a large 

 number of poorly yielding individuals, as shown in these curves. 



This graphic expression is shown in its application to wheat selec- 

 tion in the more formal or theoretical curves in figures <S, 9, K), and 

 U, based, only in a general way, on results of experiments in the field- 

 crop nurseries and field-plot tests at the Minnesota experiment sta- 



Krf cD'iOPiu-'?o:\tNcr)iooioo-.pic^-?oi-?<oh.--'*'tD(0'Ccwx*ioconp:i'ruinu'j'**L':-^XKXWirtT-^r\,-*(^0'jCWio:DC«ciriXCwii:j-iCO-iC 



£ Plant No's. 



Fig. ".—Yields, in grams, of 86 hybrid wheat plants (the same as shown in fig. 0;, arranged in 



order of yield. 



tiou. In figure 8 the solid-line curve cuts the vertical lines so as to 

 represent the individual plant yields of 100 plants of Fife wheat, and 

 the dotted-line curve does the same for 100 Blue Stem plants, arranged 

 from left to right in the order of their yield in grams. The double 

 horizontal line represents the mean between the field yields of these 

 two varieties, as averaged from numerous field trials, and approxi- 

 mately the mean between the average yields of the plants of these two 



Fig. 8.- Yields, in grams, of HXI Blue Stem and HKi Fife wheat plants compared, the broken line 

 representing the former and the solid line the latter. The mean yield is indicated by the 

 double horizontal line. 



varieties in the field-crop nursery, where each plant has an area of 10 

 square inches, one plant in a hill, with a 4 by 1-inch space allotted 

 to it. Since two standards of yield are used in these graphic expres- 

 sions, an explanation is needed. Varieties of wheat yielding 20 to 30 

 bushels per acre in ordinary field-plot culture wei-e planted also in 

 the field-crop nursery plots, where the individual plants, standing 

 singly in hills 4 by 4 inches apart and cultivated, yielded on an aver- 



