EXPERIMENTS IN FIELD PLOT TECHNIC 11 



i 



and 32 pounds for oats. The measures of variability used are the 

 average deviation, the standard deviation, and the probable error. 

 These were computed according to the following formulae : 



in which A.D. = average deviation, o-=standard deviation, E = prob- 

 able error (of a single determination), d = the deviation of a single 

 variate from the mean, and n = the number of variates. The correla- 

 tion coefficient r was determined by the formula 



n 



and the probable error of the correlation coefficient E r by the formula 



, .6745 (1 - r') 



The tests reported are of two kinds, variety tests and strain tests. 

 The variety tests were comparisons of commercial varieties, most 

 of which were taxonomically distinct. A number of pure line selec- 

 tions were included in the wheat variety tests. The strain tests were 

 comparisons of a considerable number of commercial lots of the same 

 variety obtained from different sources. These strains, so-called for 

 convenience, are not, except in a very few cases, pure lines. Some of 

 them are possibly identical, and all the strains of any one variety are 

 of course very similar, since they are taxonomically the same. 



Procedure. In the seasons of 1919, 1920, 1921, tests of va- 

 rieties and strains of oats, barley, and wheat were conducted in blocks 

 consisting of five rows ten inches apart and usually 18 feet long. 

 From 24 to 96 varieties were included in each test, and from three to 

 six (usually four) replications were used. The planting order in each 

 case was designed on a plan similar to that illustrated in figure 1. 

 It will be noted that the check plots were in continuous strips, that 

 each variety was represented in each quarter of the field, whether 

 divided from east to west or from north to south, and that in all 

 four series each variety occupied the same position with relation to 

 the check plots, and had the same varieties adjoining it on either side. 



