170 



The differences between the above lines are significant in that all three 

 came originally from the same plant. While it is admitted that these differ- 

 ences may possess very different values and may even be of different origin, 

 they are regarded as providing a valuable means of effecting improvement 

 even to the extent of producing quite new sorts. In discussing the origin of 

 these tuber variations Lundberg says "They might quite easily arise as a 

 result of certain diseases which attack certain plants but spare others; by 

 selecting those which have withstood the disease, decided progress may often 

 be made. On the other hand, variations in such vegetative parts as tubers 

 may be of a deeper nature, arising through some spontaneous change in the 

 character or 'life 'of the tuber itself. Such a phenomenon is known as tuber 

 variation. " In accordance with this point of view one of the main methods 

 of potato improvement employed at Svalof has been and now is the con- 

 tinuous selection of desirable hills and tubers. 



Pnoto by L. H. N. 



FIG. LV. Digging pedigree plots of potatoes taken from Magnum 

 Bonum, Prof. Maerker, etc. 



Another method commonly empolyed in the production of new sorts is 

 Production by means of the true seed. This seed may be obtained either by artificially 

 of sorts from cross i n g different sorts or it may be taken directly from plants in the field 

 'seed' which have been cross-fertilized naturally. The latter course has been 



abandoned at Svalof since experience has shown that success can be con- 

 fidently looked for only when plants whose values and peculiarities are known, 

 constitute the parentage. The first artificial crossings in potatoes were made 

 at Svalof in 1903 since which time the number has greatly increased. 



