EXPERIMENTS IN FIELD PLOT TECHNIC 43 



of maturity is largely responsible for strong competitive value. Then 

 in a season when earliness is closely correlated with yield a close cor- 

 relation of competition and yield is likely to be found, not because high 

 yield makes for strong competition but because the high-yielding va- 

 rieties are early. Conversely, the competing value may be dependent 

 on the yield and the correlation with earliness may be incidental, under 

 the same conditions. If the relation of earliness and yield were con- 

 stant, such a question would have little practical importance, but when 

 the relation is reversed, as it may be in different localities and even in 

 different seasons in the same locality, the relation of competition to 

 the two characteristics may be very different. The relation of compe- 

 tition to earliness and yield in these tests, therefore, may be due pri- 

 marily to the predominating influence of either of these two charac- 

 teristics, or to the influence of both. 



General conclusions regarding competition should not be drawn 

 from these tests. The problem of competition is complicated by many 

 factors, and will require numerous and extensive investigations for 

 its solution. These results, however, indicate that gross errors from 

 this source are commonly involved in variety tests, that such errors 

 occur both in rows running east and west and in rows running north 

 and south, that the error is less when the varieties and strains com- 

 pared are structurally similar than when they are widely different, and 

 that the error may be reducible to some extent by the grouping of va- 

 rieties according to the time of maturity and possibly other characters, 

 when the relation of such characters to competition is more fully 

 studied. In the present state of knowledge regarding the relation of 

 competition to the characteristics of the varieties compared, the use 

 of border rows is highly desirable, since by their use the error from 

 competition can be practically eliminated. 



SIZE AND REPLICATION OP PLOTS. 



Previous Investigation. Most of the direct evidence reported 

 on replication and size of plots has been obtained in experiments in 

 which a field of a uniformly handled crop is harvested in a large num- 

 ber of small sections. These sections are grouped to form plots of 

 different shapes and sizes, and systematically distributed sections are 

 averaged to represent replicate plots. The relative variability of the 

 yields determined by each plot arrangement is the criterion of expe- 

 rimental accuracy. Such experiments have been reported by Morgan 15 

 with wheat and fodder corn, Wood and Stratton 18 with mangels, Mer- 

 cer and Hall " with wheat and mangels, Hall and Russell 8 with wheat, 



