IMPROVEMENT OF THE POTATO. 



423 



The content of dry matter is quite variable and regularly de- 

 creases from the outside to the inside of the three zones. The 

 total nitrogen content is only slightly variable in the three zones, 

 though showing a regular increase to the inner medullary layer, 

 when calculated to the dry basis, owing to the variability of the 

 water content. Ash determinations made on ten samples varied little 

 from 0.90 percent on the fresh basis, showing that carbohydrates, 

 estimated by difference, are higher in the cortical layer, and quite 

 low in the inner medullary layer. From this we may conclude that 

 there is a difference in time of cooking in the different zones of the 

 potato, and that the glistening appearance of the cortical layer after 

 boiling would be accounted for by its larger starch content breaking 

 open the cell walls. 



SAMPLING 



Since there is such a difference in the composition of these dif- 

 ferent zones, it is extremely difficult to obtain a correct sample of 

 the tubers for analyses without spoiling them for cooking tests or 

 for planting. A number of methods were tried, the one giving the 

 most satisfactory results being that of a cylinder cut with a twelve 

 mm. cork borer, parallel to the long diameter, but a little to the 

 side. This takes in only a portion of the inner medullary layer and 

 compares well with the composition of the whole potato. The 

 greatest difference in five determinations of total nitrogen on indi- 

 vidual tubers was 0.04 percent calculated to the fresh basis. 



TABLE 4. VARIATIONS IN SAMPUNG 



This method has been used in all subsequent determinations 

 when tubers were to be used for cooking tests for planting. 



RELATIONS OF TOTAL NITROGEN CONTENT AND QUALITY 



To ascertain the relation of total nitrogen content to quality, a 

 number of tubers of the Rural New Yorker No. 2 variety in which 



