Experimental Error in Crop Tests 
11 
27. In crop breeding experiments improvement in yield 
over the original can only be measured accurately by grow- 
ing each year some of the original unselected seed for com- 
parison. The method of comparing the results of one period 
of years with those of another is unreliable. For example, 
Hogue's Yellow Dent corn which has undergone continuous 
ear-to-row breeding since 1902 yielded 39 per cent less during 
the seven-year period 1907-1913 than during the preceding 
seven years. However, a seven-year comparison with the orig- 
inal seed which has been grown as a check indicates that the 
inherent yielding power of the ear-to-row and the original 
corn are almost identical. 
28. Soil limitation may be a serious source of error in 
pot experiments. The relative total moisture-free yields for 
individual corn plants grown in pots of six sizes in 1914 were, 
in order from the smallest to the largest, 100, 211, 324.1, 
453.6, 643.8, and 747. The corresponding yields of ear corn 
were 100, 632.5, 1082.3, 2417, 2990, and 4046.7. A uniform 
application of 1.75 pound of sheep manure per plant (or 
per pot) increased the yields of total dry matter for the six 
sizes, in order from the smallest to the largest, 176.4, 95.3, 
69.3, 26.1, 12.7, and 7.2 per cent. The corresponding increases 
in yield of ear corn caused by the manure were 722.5, 193.6, 
149.2, 18.9, 14.1, and 2.9 per cent. 
In 1915 the relative yields of total dry matter from the 
six sizes of pots, progressing from the smallest to the largest, 
were 100, 150, 229.6, 355.6, 586, and 578.7 per cent. The 
corresponding relative yields of ear corn were 100, 276.2, 
819, 1647.5, 2771.3, and 2667. 
Applying manure in amounts proportional to the quan- 
tity of soil contained, in 1915 had far less striking effect 
upon the pot yields for the different sizes than when equal 
quantities were applied in 1914, regardless of the quantity 
of soil contained. 
29. When two, four, or six corn plants were grown in 
pots of the proper size for growing one normal corn plant, 
the individual plant yields of total dry matter were respec- 
tively 50.8, 26.7, and 16.6 per cent as large as for the one-rate, 
while the corresponding yields of ear corn were respectively 
39\7, 15.9, and 2.8 per cent as large. 
30. A review of several hundred experiment station 
bulletins dealing with variety, fertilizer, cultural, and pot 
