BREEDING AND SELECTION 175 



of starch, and have other desirable characteristics as, 

 suitable shape, color, depth of eyes, etc. 



Selection. Hybridizing is of small value unless 

 attended by careful selection and vigorous elimination 

 of the poorer types. All potatoes tend to vary in cul- 

 tivation, either to improve or degenerate. This varia- 

 tion is more marked in some plants than in others; 

 hence, once a variety is established, the yield may be 

 materially increased and the rapid deterioration of 

 the variety prevented by selection of the best plants. 

 Selection must be made in the field, not from the bin. 

 The whole plant must be considered, not a single 

 tuber. Goff ' showed that by perpetuating the most 

 productive and least productive plants of Snowflake 

 potatoes the total yield of the most productive one for 

 two years was 322 ounces, while that of the least pro- 

 ductive was but 100 ounces, and, summarizing fourteen 

 years' trials, the most productive plants yielded 180 

 per cent, more than the least productive. Bolley, at 

 North Dakota, found that "equal weight pieces from 

 small or large tubers of the same vine are of equal 

 value, provided all are normally mature,"* confir- 

 matory evidence that the whole plant is the unit of 

 selection. 



Growers may at least maintain the productivity of 

 their stocks of potatoes by careful selection of the best 

 plants when digging, careful storage of these tubers, 

 and then using all of them for seed. These might be 

 planted by themselves on a piece of good land, and se- 



1 (N. Y.) Geneva Report, 1887, p. 85. Wis. Report, 1899, p. 306. 



2 N. D. Bui. 30, p. 243. 



