BKEEDIISTG POTATOES. 63 



increase variation, timothy seeds from widely separated sources may 

 be mixed togetlier and seeds from the mixed ijlanting- planted in the 

 nursery. Or the stocks of seeds from separate sources may be grown 

 in the nursery and the seeds of the best selected plants may then be 

 mixed together and allowed to cross, thus giving crosses between 

 strong parent plants. In any case these cross-bred stocks may be 

 selected as under the plans given in the first part of this section. 



BREEDING POTATOES. 



Potatoes will serve as an example of a species the improved varie- 

 ties of which are propagated wholly by cuttings, the seeds being used 

 only in variety formation. The tops live only one year. The age to 

 which a variety propagated by annually planting the root cuttings of 

 a single seminally produced plant will live before the necessity of 

 renewal by sexual reproduction is resorted to is not known. But since 

 standard varieties of potatoes remain prominent for only about a third 

 of a centurj^, there is some reason for the belief that the varieties 

 reach their period of old age, or senility, in that time. 



Some of the many commonly grown varieties produce many seeds, 

 but others produce very few seeds; and under some conditions most 

 of the cultivated varieties bear very few seed balls. Doubtless those 

 best acquainted with the formation of varieties of potatoes may have 

 a knowledge of which varieties, or hybrids between which varieties, 

 have proven best to use in making new sorts. There are annuall}' 

 many new kinds created, but only a verj^ small part of 1 per cent of 

 these ever reach the prominence of commercial sorts. Luther Bur- 

 bank is quoted as saying that not more than one new variety of potato 

 in five thousand should be named and disseminated. 



The potato flower is quite open, and cross-pollination bj^ hand is 

 easily effected. The fruit, "potato ball," contains numerous seeds, 

 each of which is capable of being developed into a new variety of po- 

 tato. New varieties may be originated by planting seeds which have 

 not resulted from crossing between varieties; but the supposition is 

 that a larger iirojjortion of good kinds would i-esult were hybrid seeds, 

 fi-om hand-pollinated flowers used. 



The seeds aie planted in the open field or under glass, and when 

 several inches higli the plants nuiy be transplanted into the field, 

 wliere each plant should be in a hill by itself, each having its serial 

 number. In radical hybrids very jDoor seeds, and even plants which 

 at first appear undesirable, sometimes become the foundation of supe- 

 rior varieties. The plants do not generally gi-ow large the first year, 

 and tlie tubers are small. By discarding all the tubers of tlie poorer 

 tlu'ee-fourths of the i)lants, only the best are retained foi- planting the 

 second year. Several hills of each should be grown under proper 

 nursery-stock numbers, so as to get averag<^s, and when the tubers 



