1908.] 



IMPROVEMENT OF THE POTATO. 



437 



10. VARIATION OF THE POTATO IN CHEMICAL COM- 

 POSITION AS A BASIS FOR ITS IMPROVEMENT 



In 1902 work was started to determine whether there were 

 sufficient variations of the proteid content within a variety of 

 potatoes to warrant selection of individuals high in protein to 

 endeavor to raise the average protein content of the variety. It 

 was expected later that this work would throw some light upon Jo- 

 hannsen's theory that in "pure lines" (self- fertilized lines), fluc- 

 tuations regress completely to the mode of the pure line and not 

 toward the mode of the general population. If this is true, abso- 

 lutely no change could be made by selecting partial fluctuations. 

 Johannsen's work was not reported until after the results of these 

 two seasons had been obtained, but the data are here reported just 

 as it was collected in 1904. 



About two bushels of potatoes of uniform type were selected 

 from a carload of the variety Rural New Yorker No. 2. They 

 were all grown in the same county in Wisconsin, but it could not 

 be definitely stated that they were all grown in the same field or 

 upon the same type of soil although the latter is likely. They were 

 of good appearance and average 223 g. in weight. The smallest 

 potato used weighed 141 g. and the largest 328 g. Over one-half 

 of the tubers varied less than 30 g. from the average. The table 

 quality was good for the time of the year, it being the month of 

 May. 



Total nitrogen, dry matter and specific gravity determinations 

 were made on one hundred seventy-nine tubers. The total nitrogen 

 was determined by the regular Kjeldahl method; dry matter by 

 drying to constant weight at IO4C in a glycerol oven in a current 

 of hydrogen ; and the specific gravity by the weight in air and the 

 weight in distilled water at 2OC. Considerable variation was 

 shown in the content of the dry matter and the average was found 

 to be very low for potatoes of such good quality. This condensed 

 table shows the extent of the variation, the extremes being 15.18 

 percent and 28.27 percent. 



TABLE 14. VARIATION IN DRY MATTER IN RURAL NEW YORKER No. 2, CROP 



OF 1901 



