26 1 BULLETIN" 958, U. S. DEPARTMENT OE 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. 
