114 BREEDING CROP PLANTS 



Selection. The plant-selection method is used for the purpose 

 of isolating the best possible pedigreed strain of a commercial 

 variety. If the variety is of considerable value a large number of 

 individuals (500 to 1,000) may be selected. Often a smaller 

 number is all that the breeder can afford to test. The number 

 chosen will depend on the productive capacity of the commercial 

 variety or new introduction which is used as the basis of selection. 

 Plant selections are grown in short rows the first year, the same 

 number of seeds being placed in each row. 



Two general methods have been rather widely adopted for the 

 initial head-selection plot. In either method the same number 

 of seeds is placed in each row. The difference lies in the spacing 

 of the seeds. Some prefer to place the seeds approximately the 

 same distance apart in the row and at sufficient distance (2% to 

 3 inches) that the plants can be separately observed. Others 

 scatter the seeds in short rows, placing them so close together 

 that individual plants cannot be differentiated at maturity. The 

 latter method more nearly approximates the rod-row plan and 

 needs less room. In either case the rows are usually a foot apart. 



The field, after being carefully harrowed, is raked by hand, if 

 necessary. It is then marked out by the use of a sled marker, 

 from 7 to 12 rows being marked at a time. The rows are opened 

 with a wheel hoe and covered either with it or a rake or a hand 

 drag with numerous iron teeth. 



Those selections which by field inspection seem to be of inferior 

 vigor, to have weak straw or other undesirable characters, are 

 eliminated before harvesting. A few others are discarded on 

 the basis of yield, although the experimental error in a yield 

 comparison of this kind is much too large to justify rejection. 

 The following year each selection may be grown, if sufficient 

 seed is available, in three systematically distributed 18-foot 

 rows, 1 foot being removed from each end of every row before 

 harvesting. 



According to Love and Craig (1918a), J. B. Norton, of the 

 United States Department of Agriculture, was the first to put 

 the rod-row method into general use. By varying the length 

 of the row and obtaining the yield in grams it is possible to con- 

 vert yields into bushels per acre by multiplying by a simple 

 conversion factor. If the length of oat rows harvested is 15 ft. 

 and the yield is obtained in grams, the yield per acre in bushels 

 may be obtained by multiplying by 0.2. For wheat and barley, 



