348 



The Journal of Heredity 



bins in the spring the requisite amount 

 of seed, using tubers having the desired 

 shape and size but without knowledge of 

 whether they came from high yielding 

 strains or not. This method of choosing 

 seed from year to year, using merely 

 the best tubers without a knowledge 

 of their ancestry or obtaining a test 

 of their producing power, is known as 

 'mass-selection.' This method will in- 

 evitably lead to imi^rovement because 

 the very poor hills will not produce good 

 tubers, and hence will be eliminated. 

 But the improvement is a very slow one. 

 In emjjloying this method of mass 

 selection, growers were working blindly 

 without knowing how or when or even 

 whether they were going to reach a 

 stability of type." 



Intelligent breeders have now dis- 

 carded this method of picking the best 

 tubers out of the bin without knowing 

 anything about their jjasl. In its 

 place they use the method of pedigree- 

 breeding, picking out the best hills for 

 perpetuation, instead of the best single 

 potatoes. The growtr should have a 

 vivid mental picture of the standard 

 toward which he is working, and then 

 should choose his seed-potatoes from 

 those hills which, as a whole, most 

 nearly meet his ideal. 



Ideals for the perfect ]jotatoes natur- 

 ally vary with localities, but certain 

 attributes are universally desired. 

 Among these are: 



1. High yield. This means not only a large 

 number of potatoes per hill, but a large number 

 of large potatoes, few or no small ones. 



2. Good quality. For culinary use, this 

 means a large amount of starch, which makes 

 the potato mealy when cooked. 



3. Disease-resistance. Particularly in the 

 Eastern United States, diseases are a serious 

 hindrance to potato growing. There are no 

 varieties that are disease-proof, but some are 

 much more resistant than others. 



4. Good kecj)ing fiualities. Potatoes must 

 often be stored for a long time before they are 

 used. 



5. Good color of flesh and skin. In general, 

 a yellow skin and white flesh are desired, but 

 the South prefers a pink-skinned variety. 



6. Skin of good texture. Buyers seem to 

 think that a netted and slightly rough skin 

 is to be preferred as indicating j)roper maturity 

 and good quality. 



7. Tubers of good shape. Flat-round or 

 flat-oval potatoes are preferred to oval or 

 cylindrical. 



8. Shallow eyes, relatively few in number. 

 This saves waste in peeling and lessens decay. 



9. Proper length of season. Some varieties 

 mature in seventy days after planting, others 

 require 200. 'J'he grower must have a variety 

 suited to the length of his local season. 



10. Upright, vigorous plants. In general, a 

 wide-spreading plant takes up more room 

 and is more expensive to spray. 



1 1 . Thick-skinned leaves. These are not 

 so easily penetrated by disease-spores. 



12. No tendency to "second growth." 



13. Trueness to type of variety grown. 



With a definite knowledge of the 

 kind of potato he wants, the grower 

 will dig enough hills by hand to find 

 some of his best, that conform to his 

 ideal, and he will save the potatoes from 

 these hills for his next planting. If 

 he is going at it scientifically, and plants 

 on a large scale, it will pay him to grow 

 this seed for a few years and select 

 the best each year for planting.^ But 

 most farmers will probably content 

 themselves with picking out good hills 

 for next year's crop. These may be 

 chosen either by weighing the total 

 number of potatoes produced, or by 

 counting. If the season has been an 

 average one, hills which contain six or 

 more good tubers are saved for planting. 

 In a poor year it may be necessary to 

 use hills which contain only five; in a 

 good year the standard may be raised 

 to seven. There is no attempt at 

 pedigree breeding by kee]jing the differ- 

 ent strains separate. All hills meeting 

 the established standard are thrown 

 together and saved for seed. The next 

 year these are planted; in the fall the 

 process of selecting the best hills is 

 repeated. This method will gradually 

 eliminate the poor strains and raise the 

 average yield of the cro]) very rapidly. 

 The first year, perhai)s only 5 or 10% 

 of the hills will be found to have j^ro- 

 duced as many as six good tubers; the 

 second year this percentage should be 

 more than doubled; while after three 

 years of selection, six marketable pota- 

 toes should be found in a fourth or a 

 third of all the hills in the field. 



' Full details of a method worked rmt by Dr. H. J. Webber, secretary of the Research Com- 

 mittee on plant breeding of the American Genetic Association, are given by Dr. Gilbert (pp. 63-69). 

 This method is said to have been remarkably successful. 



