Plant-Breeding for Farmers. 169 



and if fifty tuber-units were selected there will be 500 tubers to plant 

 which will make a total of 2000 hills in the breeding-plot. The land 

 used for this breeding-plot should be carefully selected for uniformity, 

 as variations in the land will modify the comparative yield and is liable 

 to render the results untrustworthy. Number each row of forty hills 

 with the number given the tuber-unit of the preceding year. It is de- 

 sirable for comparison to plant about every tenth row with unselected 

 seed of the same variety, cut and planted in the same way, but without 

 reference to keeping each tuber separate. The production of these check- 

 rows will show whether progress is being made in the selection. 



Cultivate the breeding-plot and treat it otherwise just as an ordinary 

 crop is treated. 



Making the second year's selections. — -When the breeding-plot nears 

 maturity the individuals should be examined and either the best and 

 healthiest vines marked, or if easier, the diseased vines showing weakness 

 marked, so that they can be discarded later. Then dig each tuber-unit 

 as in the preceding year placing the tubers from each four-hole unit to- 

 gether at the side of the row. Each unit should then be weighed and the 

 number of large, medium and small sized tuber recorded. This will 

 enable the breeder to determine which of the original fifty tuber-units 

 selected in the first year has given the largest average yield in the ten 

 tuber-units or forty hill test, and this is the primary test of the value of 

 the original selection. Following the same method as used the first year, 

 select from the breeding-plot the fifty best tuber-units, and preserve 

 the tubers of each unit separately in a paper bag. The majority of the 

 selection in this year should naturally be made from those rows which 

 have given the highest yield. Number the tuber-units selected in this 

 second generation i-i, 1-2, 1-3, and 2-1, 2-2, etc., according to the 

 scheme of numbering individual selections described in early part of this 

 bulletin, page 142. These numbers can be placed on the bags and notes 

 on weight of yield, number of tubers per unit, etc., recorded under the 

 same number. 



All of the good tubers from the remaining tuber-units of the breeding- 

 plot not selected should be retained for planting a mutiplication-plot the 

 third year which should furnish sufficient seed for planting the general 

 crop for the fourth year. 



At some convenient period, before planting time, as in the preceding 

 year go over the product of each select tuber-unit and pick out the ten 

 best tubers of each for the next year's planting. 



Third year's selections. — In the third year, the fifty selections of 

 heavy yielding tuber-units should be planted by the same methods used 

 the second year, forty hills at least of each selection being planted. The 

 row from each unit should be plainly labeled or otherwised marked to 

 avoid mixing the pedigree. Treat this breeding-plot as described for the 



