6 



BULLETIISr 958, U. S. DEPAETMEIsTT OF AGRICULTURE. 



individual hUls had been completed and dividing the population into 

 25-grani classes.^ The results are shown in Tables I, II, and III. 



Table I. — Rate of development of potato tubers at Greeley, Colo., in 1916 and 1917. 

 [Data from 200 hiUs of the Rural New Yorker variety dug at 1-week intervals during each season.] 





Time 

 after 



plant- 

 ing 



(days). 



Num 



ber of 



Marketable 



tubers 

 (per cent). 



Weight (grams). 



Date of digging. 



tubers. 



Total. 



Average. 



Largest — 



In- 





Total. 



Average 

 per hill. 



Num- 

 ber. 



Weight. 



Per 



tuber. 



Per 

 hiU. 



Tuber. 



Hill. 



per 

 hiU. 



Season of 1916: 



Aug. 24 



Aug. 31 



Sept. 7 



Sept. 14 



Sept. 21 



Sept. 28 



Oct. 5 



72 

 79 

 86 

 93 

 100 

 107 

 114 



64 

 71 

 78 

 85 

 92 

 99 

 106 

 113 

 120 

 127 



1,085 

 1,151 

 1,220 

 1,169 

 1,295 

 1,125 

 1,048 



863 

 870 

 922 

 957 

 960 

 987 

 928 

 984 

 935 

 931 



5.4 

 5.8 

 6.1 

 5.8 

 6.5 

 5.6 

 5.2 



4.32 

 4.35 

 4.61 

 4.79 

 4.80 

 4.94 

 4.64 

 4.92 

 4.68 

 4.66 



2.4 

 34.8 

 49.6 

 65.3 

 66.4 

 71.4 

 75.5 



7.1 

 61.2 

 80.1 

 91.7 

 91.7 

 94.1 

 95.4 



37,235 

 79,028 

 114, 361 

 150, 987 

 179,480 

 193,637 

 197, 123 



10,843 

 31, 579 

 65,064 

 107, 746 

 142, 470 

 162, 745 

 186, 460 

 218, 035 

 222,055 

 228, 755 



34.3 



68.7 

 93.7 

 129.2 

 138.6 

 172.1 

 188. 1 



12.6 

 36.3 

 70.6 

 112.6 

 148.4 

 164.9 

 200.9 

 221.6 

 237.5 

 245.7 



186.2 

 395.1 

 571.8 

 754.9 

 897.4 

 968.2 

 985.6 



54.2 



157.9 



325.3 



538.7 



712. 4 



813.7 



932.3 



1,090.2 



1,110.3 



1, 143. 8 



160 

 299 

 417 



715 

 631 



852 

 853 



55 

 180 

 255 

 409 

 735 

 582 

 815 

 903 

 991 

 875 



418 

 856 

 1,135 

 1,449 

 1,861 

 1,826 

 2,079 



142 

 366 

 670 

 1,105 

 1,480 

 1,745 

 2,270 

 2,100 

 2,280 

 2,020 



176.7 

 183.1 

 142.5 

 70.8 

 17.4 



Aug. 16 



Aug. 23 



Aug. 30 



Sept. 6 



Sept. 13 



Sept. 20 



Sept. 27 



Oct.4 



Oct. 11 



Oct. 18 







5.2 

 33.2 

 59.9 

 70.0 

 69.1 

 73.5 

 74.1 

 79.4 

 79.7 





 14.7 

 60.2 

 87.0 

 95.7 

 96.2 

 97.3 

 97.0 

 97.6 

 97.7 



"'i63.'7 

 167.4 

 213.4 

 173.7 

 101.3 

 118.6 

 157.9 

 20.1 

 33.5 



A study of the data presented in Table I brings out many points of 

 interest. It will be seen that practically the entire crop of tubers was 

 set at the beginning of the period of tuber development, probably 

 within the space of a very few days. The data, however, show a slight 

 increase in the number of tubers up to and including the third digging, 

 in September; also a decrease after that period, so that the numbers 

 at the beginning and at the end of the sampling period are very 

 nearly the same. A possible explanation of this fluctuation is that 

 the numbers employed may not have been large enough to eliminate 

 the so-called experimental error. On the other hand, it seems quite 

 probable that the small increases indicated in the records as occurring 

 early in the season were actual. Toward the end of both seasons it 

 was observed while digging the hills for the statistical studies that 

 some of the very small tubers slightly below half an inch in diameter 

 had shriuik considerably, and occasional evidences of the almost 

 complete disintegration of these small sizes were found. If this con- 

 dition occurred in tubers originally above the half-inch size, which 

 would have been saved and counted at the earlier dates of sampling, 

 it would account for the apparent decrease in the number of tubers 

 toward the end of the season. Further studies are needed to deter- 

 mine whether this is the cause. 



In both years there was an increase in the weight per hill and ia 

 the average weight per tuber throughout the entire period of the 



2 Twenty-five grams are about equivalent to 0.88 ounce avoirdupois. 



