Experimental Error in Crop Tests 
49 
The quadrates were accurately laid out by means of an 
iron frame, as shown in the following figure. A rectangular 
frame is more reliable than a round one where the grain is 
planted in rows. 
Frame used for laying off quadrates (Table 26) 
Because of severe and variable winterkilling the 14 plats 
differed markedly in the percentage of plants surviving, and 
in yield. There was also much greater variation between 
the quadrates within a single plat than would normally be 
expected. 
Opportunity was provided to compare the mean results 
of 5, 10, and 20 systematically distributed quadrates with 
the entire plat from which they were harvested. In making 
four groups of five quadrates each, group (a) contained quad- 
rates Nos. 1, 6, 9, 14, and 17; group (b) contained Nos. 3, 
8, 11, 16, and 19 ; group (c) contained Nos. 2, 5, 10, 13, and 
18; and group (d) Nos. 4, 7, 12, 15, and 20. For two groups 
of 10 quadrates each, group (a) contained Nos. 1, 4, 5, 8, 9, 
12, 13, 16, 17, and 20, and group (b) contained Nos. 2, 3, 6, 
7, 10, 11, 14, 15, 18, and 19. The results of these various 
groupings are shown in Table 26 in comparison with the yields 
of the entire respective plats. 
The average yield determined from 20 quadrates deviated 
1.4 bushels from the average plat yield. 
For individual plats the 20-quadrate yield estimation 
varied from 0.2 to 3.2 bushels per acre. 
Smce each kind of wheat was grown in duplicate plats 
the mean of 40 quadrates can be compared with the mean 
of two field plats. In this comparison the average of these 
