PLANT IMPROVEMENT 



157 



The yield may be increased further by crossing. The 

 result of the ear-to-row tests is really the separation of high- 

 yielding strains from a mixture of low, medium, and high- 

 yielding plants. Experiments made under the direction of 

 the Connecticut Agricultural Experiment Station have 

 shown that an increase of as much 

 as ten bushels per acre may be 

 secured by using seed produced 

 by the crossing of two high-yield- 

 ing strains, as compared with 

 the yield of either parent alone. 

 In farm practice, all that is neces- 

 sary is to plant alternate rows of 

 two high-yielding strains that 

 have been developed by the ear- 

 to-row test. The seed thus pro- 

 duced is used for the next year's 

 planting. A separate plot of each 

 pure strain must be maintained in 

 order to keep up a supply of seed 

 for future crossing. 



A recent modification of this 

 plan has even greater promise. It 

 is essentially a double cross. Two 

 pairs of high-yielding strains are t 

 crossed. The plants resulting from this cross are recrossed. 

 Seed from these plants produce a strain of corn of higher 

 yield than the original stock. After the final strain has been 

 established it may be maintained by ordinary careful methods 

 of selection. 



While the method of improvement just outlined may seem 

 somewhat difficult, it really requires but little time and effort. 



Diagram showing double cross 

 of corn to secure increase in 

 yield. 



A, B, and C, D are ears of 

 high-yielding strains selected 

 by ear-to-row method. 



A and B are crossed, produc- 

 ing E. 



C and D are crossed, produc- 

 ing F. 



E and F are then crossed, pro- 

 ducing G, H, I, J, K, etc. 

 These ears furnish seed for 

 general planting, producing 

 maximum yield. 



