Constituents of Potato Tubers. 361 



gravity; in fact in factory practice Marker's 1 table of specific 

 gravities is commonly used in assaying potatoes for starch. Also, 

 the starch content and dry matter are correlated positively with 

 mealiness, whereas high protein causes sogginess. According to 

 American standards mealiness is desirable; in Europe the reverse 

 is true. Therefore it would seem that attempts to develop a high 

 protein potato and still to maintain desirable culinary properties 

 were doomed to failure, although East 2 was convinced otherwise, 

 provided a high dry- matter content be maintained. 



In 191 1 56 samples of potatoes, representing 4 varietal groups, 

 and grown under various conditions in different parts of Minne- 

 sota, were collected and analyzed at this station, with a view to 

 determining the factors which affect the composition. It seemed 

 desirable to utilize these data still further by calculating the co- 

 efficients of correlation among all the constituents of the tubers. 

 The results of these calculations appear in Table I. Both starch 

 and soluble sugars were determined, but the sum of the two only 

 is here presented. The starch represents about 95 per cent, of the 

 two. 



It will be seen that there is an intimate relation between spe- 

 cific gravity and dry matter, which is to be expected. It will be 

 further noticed that there is no correlation whatsoever between 

 carbohydrate and dry matter and between nitrogen and dry mat- 

 ter. This is not contrary to the relation stated above between 

 specific gravity and starch, since in factory practice the starch 

 content is considered on the wet basis, and in this table all calcu- 

 lations are on the dry basis. The nitrogen and carbohydrate vary 

 inversely with each other, which is naturally the case with the 

 two main constituents of a tissue, totaling 80 per cent, of the dry 

 matter. Also as the dry matter increases the ether extract in- 

 creases, and the ash decreases. 



These relations can be stated in another way: A higher dry- 

 matter content does not simply mean a loss of moisture, else there 

 would be no change in the ratios of constituents. The formation 

 of a higher dry matter content means the laying down of more 

 ether extract material, as evidenced by the coefficient of -f- .333 



1 Marker, M. H., Landw. vers. Stat., 1880, xxv, 107. 



1 East, E. M., III. Agr. Exp. Sta., 1908, Bull. 127, p. 135. 



