286 



Journal of Agricultural Research 



Vol. XVIII. No. s 



The difference in resistance to puncture by mechanical means in these 

 three varieties of potatoes is very marked; and it was considered of in- 

 terest to see if there was correlated with it some variation in the chemi- 

 cal composition of the tubers, especially in the constituents of the cell wall. 

 Accordingly, determinations of the pentosan and crude fiber content of 

 the two regions, cortex and central portion, of potatoes of each of the 

 three varieties were made. 



In preparing the samples ior analysis the potato was cut into slices 

 about 8 mm. in thickness, a thin peeling removed with a sharp knife, 

 and the cortex sliced away. This was dried, ground, and analyzed. 

 The central portion of the potato after the ring of bundles had been peeled 

 off was treated in like manner. Pentosan and crude-fiber analyses were 

 made and were calculated to dry weight, the dry weights being obtained 

 in the usual way by drying to constant weight in a vacuum oven. 

 Duplicate determinations were made. The data obtained from the 

 analyses are given in Tables VIII and IX. 



Table VIII. — Pentosan content of cortex and interior tissue of potatoes 

 [Expressed as percentage of dry weight] 



Table IX. — Crude-fiber content of cortex and interior tissue of McCormick, Bliss 

 Triumph, and Green Mountain potatoes 



(Expressed as percentage of dry weight] 



From Table VIII it is evident that the pentosan content of the cortex 

 of McCormick potatoes is somewhat higher than that for the other two 

 varieties. The pentosan content of the central portion, however, seems 

 to be somewhat lower in this variety. In Table IX is shown the crude- 

 fiber content of the three varieties. McCormicks are higher in crude-fiber 

 content than either of the other varieties. In the cortex of the McCor- 

 micks there is over 50 per cent more crude fiber than in the same region 

 of the other two varieties. The interior also of the McCormick tubers 



