190$.' 



IMPROVEMENT OF THE POTATO. 



435 



9. Degree of maturity. In 1902, a number of potatoes of 

 Rural New Yorker No. 2 variety, of different degrees of maturity, 

 were analyzed. The determinations showed that the greater part 

 of the total nitrogen is developed early in the growth of the tuber, 

 while the starch is stored up later. A microscopical examination 

 showed that the starch grains in the cells of the immature tubers 

 are small in size and few in number. Starch grains in the cortical 

 and outer medullary layers of mature tubers averaged about 75 

 /*. and were found as large as 105 /*. ; while in immature tubers 

 of less than an ounce in weight, the starch grains averaged only 



2 5 f" ' i i , 



TABLE 13. COMPOSITION OF TUBERS OF DIFFERENT DEGREES OF MATURITY 

 AVERAGES OF A NUMBER OF TUBERS 



These tubers, as might be expected from their composition, 

 increased in desirability for table use with maturity to such an 

 extent that we may conclude that all immature potatoes should be 

 rejected for cooking. 



This fact seems a reasonable explanation of the influence that 

 certain other minor factors seem to have on quality, such as dis- 

 tance apart and time of planting, depth and frequency of cultiva- 

 tion, etc. In fact any and all of the conditions of environment 

 that lead to the normal development of healthy, mature potatoes 

 may be considered as contributing toward their table quality. 



As a result of these tests, we are led to the following conclu- 

 sions regarding quality : 



i. Quality depends upon the following factors: a. Homo- 

 geneous anatomical structure. In general, quality increases with 

 the thickness of the cortical layer, and decreases as the number 

 of eyes increases. A variety shape which gives a chance for a 

 large ratio of cortical to inner medullary layer, is an advantage 

 b. Dry matter content. This must be such that the cooked starch 

 fills the cells to their bursting point. The lower limit is roughly 

 estimated at 18 percent, c. Maturity. This is affected by all 



*Weig-hts of the different classes were approximately 50 jr., 909 g-., 150 g-. and 250 g. 



