179 



introduced about 150 years ago, yet is still one of the best sorts grown in that 

 Province (59, p. 28). The opinion held at Svalof regarding this important 

 question is that there is no period oj old age in a variety oj potatoes. 



The degeneration which is often noticed is believed to be due to certain 

 factors which hinder the normal development of the plants and tubers or 

 which invite disease. Potatoes reach their highest state of vigor and develop- 

 ment under cool, moist conditions. Seed tubers produced under such con- 

 ditions almost invariably give better results than do those grown in hotter 

 and drier regions, owing it is thought to their greater vigor. Where potato 

 growing is prosecuted in districts which are unfavorable to the production 

 cf strong vigorous seed tubers it is considered good practice to obtain seed 

 at frequent intervals, from districts which are more favorable to this crop. 

 Where this practice is not followed the vigor may gradually become weakened 

 resulting in a corresponding depreciation in yield and quality. Similar 

 results may likewise follow neglect, even in the best districts, to discriminate 

 between small, poorly developed and sound seed tubers. Too often all 

 the good sound tubers are sold or used for cooking while the poor, discarded 

 and in many cases diseased tubers are kept for planting. Where this practice 

 is followed there is bound to be a falling off in productiveness. The evidence 

 at present available seems to show that where suitable sorts are used and where 

 suitable tubers oj these sorts are utilized for seeding purposes each year, the 

 standard of a variety may be maintained indefinitely under all favorable conditions 

 oj soil and climate. Since some varieties are not adapted to certain condi- 

 tions it is quite possible that their power to resist disease may become gradually 

 reduced. This would seem to explain why certain varieties grown in com- 

 parison with others and under similar conditions for a number of years seem 

 to be more susceptible to blight and other diseases than do neighboring 

 sorts. Obviously, the main considerations are maintenance of vigor and 

 control oj disease, and this implies very careful choice of seed tubers, careful 

 cultivation, spraying and rotation of crops. In Sweden special emphasis is 

 laid upon the latter point. The need for care in this regard is considered 



even greater with potatoes than with the cereals. 



i 



The yields and starch content of the different potato sorts investigated Results 

 at Svalof up to and including 1910, have recently been made public in an obtalned in 

 excellent summary of the work in potato breeding by Lundberg (24) . The ? ' 

 following tables are taken from this publication: 



