26 BULLETIN 958, U. S. DEPAETMEISTT OF AGRICULTURE. 



mately 80 days after planting. At this time nearly one-third of the 

 total period of tuber development had been completed. 



The differences in the sizes of tubers in the individual hill are 

 attributed largely to the unequal rate of growth rather than to 

 differences in the age of the tubers. 



A small increase in the weight of tubers was found to occur after 

 the vines had been killed by frost. 



■ The weight of the tuber does not appear to be correlated with the 

 length of the stolon upon which it is produced. 



The average data show a tendency toward a decrease in the size 

 of the tuber on the upper stolons, though the individual plants showed 

 considerable diversity in this respect. 



The number and the weights of tubers per hill were found to be 

 influenced by the size and the kind of the seed piece planted. 



Well-defined differences were found in the tuber-producing capac- 

 ity of different varieties when grown under similar conditions. 



The experiments on different types of soil showed that a close 

 relationship exists between the character of the soil and the number 

 and the weight of tubers. The largest numbers and weights were 

 produced on the lighter types of soil. 



The irrigation experiments, while not carried to a final conclusion, 

 indicated that the application of water before tuber formation had 

 begun increased the number of tubers. Increasing the number of 

 irrigations appears to have had little effect on the number of tubers. 

 The weight per hill, however, was increased by each additional 

 irrigation except where the applications were too frequent. 



