DEVELOPMENT OF TUBERS IN THE POTATO. 7 
investigation. In 1916 the percentage of marketable tubers with, 
respect to both number and weight increased up to the end of the 
season, while in 1917 the number percentage remained nearly con- 
stant after October 11 and the weight percentage after September 27. 
Fig. 4.— Young plant of the Irish Cobbler variety of potato, showing its root system and the starting 
of stolons. The plants shown in figures 4 to6 were grown by and photographed under the direction of 
W. V. Shear. 
The rate of growth was found to be very rapid during the early 
part of the period of tuber development. The largest increases per 
week (208.9 and 213.4 grams in 1916 and 1917, respectively) were 
at the rate of approximately 30 grams (1 ounce) per hill for each day. 
