DEVELOPMENT OF TUBERS IN THE POTATO. 



21 



A study of Table VII shows that both the number and the weight 

 of tubers per hill varied directly with the size of the seed piece 

 planted. There was also a corresponding increase in the number of 

 stems per hill. If, however, we consider the stem rather than the 

 hill as the unit for comparison, we find that the number of tubers 

 which set per stem was affected in only- a very small degree by the 

 size of the seed piece, though the general trend was toward a slight 

 decrease in the number of tubers produced as the size of the^seed 

 increased. The effect on the weight of the tubers per stem was 

 much more pronounced, as there was a very consistent and well- 

 defined decrease associated mth increase in the size of the seed. 

 It is apparent that the food supply was not sufficient to maintain 

 the needs of the increased number of_ stems for maximum tuber 

 production. . _ ' _LV 



Table VIII. — Relative influence of whole and cut seed on tuber production as shoivh b)j 

 the results with different kinds of seed where seed pieces of the same weight were used in 

 tests of the Rural New Yorker variety of potatoes grown at Greeley, Colo., in 1916 and 

 1917. 



Size and kind of seed. 



Weight 



of seed , Number 

 piece I of stems 

 planted I per Mil. 

 (ounces). 



Number of tubers. ^'^^f?J;?I\"^^" 

 (grams). 



Per hill. Per stem. PerhUl. Per stem. 



1 ounce, whole i 



2 ounce, hEilved ^ 



4 ounce, quartered | 



2 ounce, whole 1 



4 ounce, halved / 



3 ounce, whole i 



6 ounce, halved / 



- - I 



3 ounce, halved \ 



<i ounce, quartered / 



.»{ 



1.76 

 1.81 

 1.63 



2.60 

 2.50 



3.22 

 3.05 



2.25 

 1.96 



4.25 

 3.99 

 3.63 



6.31 

 5.29 



7.18 

 6.28 



4.79 

 4.13 



2.41 

 2.20 

 2.23 



2.42 

 2.12 



2.23 

 2.06 



2. 12 

 2'u 



712. 72 

 668. 61 

 673. 25 



876. 55 

 815. 51 



886.23 

 836.54 



764.90 

 737. 56 



404.80 

 368. 89 

 413. 20 



336. 74 

 326. 65 



274. 85 

 274. 14 



339. 32 

 375. 95 



Comparisons of; the results obtaiiied from whole and cut seed 

 recorded in Table VIII show a slightly larger number and, with one 

 exception, a larger weight of tubers per stem where whole seed was 

 used. - 



RELATION OF VARIETY TO TUBER PRODUCTION. 



It is a matter of common observation that the tuber-producing 

 abihty of different varieties varies considerably with respect to the 

 number and the weight of tubers per hill as well as other character- 

 istics. This is brought out very clearly in the curves shown in 

 figures 9 and 10. The data on which these are based were obtained 

 in 1915 from 500 hills each of the Pearl and Rural New Yorker 

 varieties taken from adjacent plats which were grown under condi- 

 tions as nearly identical as possible. 



A study of the curves for the number of tubers (fig. 9) shows an 

 entirely different distribution for the two varieties. In the Rural 



