173 



number of sorts are continually being originated from this cross-bred seed. 

 In view of the numerous combinations which are possible from a single 

 crossing the production of new sorts is quite a simple matter. The obtaining 

 of something better, however, is an entirely different and an immensely more 

 difficult problem. 



Another important quality in the potato, which is investigated carefully Starch deter- 

 at Svalof and other Scandinavian centres, is the starch content of the tuber, mination. 

 since this is regarded as a sort character of importance. The determination 

 of starch naturally has its greatest value when sorts for the manufacture 

 of the commercial product are being sought. In this case the actual 

 quantity oj starch per acre is the basis of valuation. In cooking potatoes, on 

 the other hand, high starch content is not of great importance but rather 

 is likely to be the reverse as it may be inimical both to taste and cooking 

 quality. As a general aid in the work, however, the determination of starch 

 content has proven of great assistance. 



On account of the diminutive size of the sample available for testing 

 from each sort, "Stohmann's" method of analysis has been used. This 

 method is briefly as follows: A number of tubers from a given lot are taken 

 and weighed after being thoroughly washed and dried. They are then 

 dropped into a glass jar of water so equipped' as to indicate exactly the 

 water displacement. In this way the specific weight is quickly obtained. 

 Since the specific weight of potato tubers has been found to stand in very 

 close relationship to the starch content, a scale has been devised which 

 indicates at a glance the per cent of starch contained in tubers of a given 

 weight. 



The starch content of potatoes is greatly influenced by soil and seasonal 

 conditions. During dry years it is usually higher than during moist years. 

 This is believed to be due to the difference in the inner development of the 

 tuber during different years. Great variation in the starch content of a 

 given sort is also induced by soils of different character. Since some sorts 

 are better suited to certain soils than are others, the problem of how to cor- 

 rectly interpret starch determinations becomes a complicated one. 



In his investigations in connection with this problem Lundberg has 

 found differences in the starch content of single plants belonging to the 

 same pedigree sort. These he believes to be due to factors other than those 

 which are external. As an example of this sort of variation may be cited 

 the results of investigation with the two well known sorts Magnum Bonum 

 and Wohltmann (23 p. 94.) . The material for this investigation came in each 

 case from a single plant chosen on the basis of form of tuber and general 

 appearance of plant. The following table indicates the results of the 

 analysis: 



