60 



BREEDING CROP PLANTS 



series then replication becomes a matter of systematic repetition 

 as is shown by the following diagram in which each different letter 

 represents a distinct strain. 



A METHOD OP REPLICATION 



ABCDEFGHABCDE.FGHABCDEFGHABCDEFGH 



As a rule the experimental plots cannot all be placed in the 

 same series. It is often necessary to make alterations from a 

 mere systematic repetition in order to secure a representative dis- 

 tribution of the strains. The two following diagrams illustrate 

 a correct and an incorrect manner of replication: 



CORRECT MANNER OF REPLICATION 



INCORRECT MANNER OF REPLICATION 



Size of Plot. The number of replications required to secure 

 a given degree of accuracy is somewhat dependent on the area 

 of the plot. Mercer and Hall (1911) found that variability is 

 diminished with increased size of plot up to J4o acre. Plots of 

 larger area do not show the same relative reduction in variability. 

 Fig. 13 presents graphically their results with wheat. 



Montgomery (1913) also finds that increased size of plot, 

 up to a certain limit, rapidly decreases variability. In plant- 

 breeding work where very numerous strains are compared, the 



