42 POTATO* DEVELOPMENT WORK IN WISCONSIN. 



studies undertaken by the Office of Horticulture U. S. Depart- 

 ment of Agriculture in 1911 and 1912 rather more marked differ- 

 ences were obtained in a comparison between high and low yield- 

 ing hills, or more strictly speaking between healthy and weak 

 plants. The data obtained showed an average yield from twelve 

 healthy tuber units of as many different varieties of 3.2 Ibs. 

 primes and 1.77 Ibs. culls or a total of 4.97 and of .2 Ibs. primes 

 and .68 Ibs. culls, a total of 0.88 Ibs, from a similar number of 

 weak units of the same varieties as the healthy. To recapitulate 

 the data, the healthy plants averaged 3.2 Ibs. of primes as against 

 0.2 Ibs. from the weak plants; and a total production of 4.97 Ibs. 

 as against 0.88 Ibs. or ovor five times as much total crop and 16 

 times as much weight of marketable sized tubers. 



These two examples would seem to give ample justification for 

 the statement which I have previously made that the greatest 

 immediate gain secured by selection comes through the elimina- 

 tion of the weak and unproductive plants. 



THE TUBER UNIT METHOD. 



As previously stated the tuber unit me 1 1 mil differs from hill 

 selection in only one particular and that is in the method of mak- 

 ing the original selection. The first step in this method is to sel- 

 ect from the seed bin a considerable number of tubers of from to 

 6 to 9 oz. in weight, which most nearly approach the type of the 

 variety to which they belong. These tubers are then planted at 

 the proper time on the tuber unit plan as previously described 

 under ' ; hill selection. ' ' From this point on the process is identi- 

 cal to that outlined for hill selection. In taking notes upon the 

 tubers, each set of fours is judged as an individual entity and 

 dealt with accordingly. If the season has been a normal one it 

 will be unnecessary to plant the tubers of the selection separ- 

 ately the second year as suggested for the hill selections. If 

 however the season has been unfavorable I would advise plant- 

 ing the following season 011 the tuber unit basis. When a de- 

 sirable strain has been secured proceed to increase it for field 

 planting. Do not on any account relax your watchfulness over 

 your selections. If weak plants appear they should be re- 

 moved prior to harvesting the crop. The vigor and produc- 

 tiveness of r, variety can only bo maintained by eliminating all 

 the weak and diseased plants. If you are growing seed pota- 



