NO. 572] THIRTEEN TEARS OF WHEAT SELECTION 465 



fluctuations from year to year agree very closely. These 

 data indicate that increased yield is due to favorable 

 environmental factors and not to improvement by 

 selection. 



A comparison of the yield of each variety for the first 

 five years of the test with that of the last five years is 

 shown in Table V. The data in this table show that 

 there is no significant difference in yield for these two 

 periods. In Russian and Polish (1) there is a slight 

 increase in favor of the latter period, but in the other 

 four varieties there is just as much decrease for this 

 period. However, there is not enough difference in any 

 case to indicate either permanent improvement or de- 

 crease in yield. As far as these varieties are concerned, 

 it seems that selection has brought about no permanent 

 improvement. 



TABLE V 

 Five-year Period 



A curve of the yields of the six varieties under con- 

 sideration for the thirteen years of the test was plotted 

 and a straight line was fitted to it, by the method of the 

 least squares, to indicate the trend of the yield. This 

 curve is shown in Plate I. There is a slight downward 

 tendency in this straight line, but it is not enough to indi- 

 cate a tendency toward decrease in yield. The line fitted 

 to the curve of height (Plate III) also shows a slight 

 tendency downward. 



The data herein cited are not sufficient for definite con- 



