176 



The above table serves to reveal not only differences between different 

 tubers produced by the same plant, but differences between the different 

 plants and between the different sorts. The variation within 349 for example, 

 is clearly much greater than that within 2172 or Magnum Bonum. It will 

 also be noted that the size of the tuber seems to have very little influence 

 on the per cent starch, although small potatoes are not infrequently low 

 in this material owing, no doubt, to their imperfect development. 



In view of the above behaviour of individual tubers and individual plants 

 in respect of starch content great care must be taken in the choice of material 

 for analysis. Only "pure-lines" can be investigated to any purpose and 

 of these, representative hills must be taken. 



Field trials of The field trials of potato sorts at Svalof are laid out in two series. The 

 potatoes. fi rs t i s called the small or preliminary sort trials, and the latter the large 





Photo by L. H. N. 



FIG. LVIII. Digging comparative trial plots of potatoes and taking notes on character 

 and condition of the tubers. Note stakes placed at hills during growing season 

 on account of some peculiarity of growth or evidence of disease. 



comparative sort trials. The first series accommodates the newly produced 

 sorts including seedlings and those which have been isolated by selection 

 from an ordinary variety. The second series receives the most promising 

 sorts and makes the final pronouncement upon them. 



In the preliminary trials eight whole tubers of each sort are planted. 

 This makes eight hills. For the sake of convenience these eight hills are 

 arranged in two rows of four hills each. During the growing season careful 

 notes are taken as to the uniformity, character, attitude toward disease 

 and general behaviour of each sort, and on this basis many exclusions are 

 made. 



The large comparative sort trials are laid out more systematically and 

 in a manner very similar to that followed with the other crops operated with 



