I 
1 *0T A'l'O T N N ES^i'K^VTlO X S 
25 
included. These corrections, which are for the purpose of eliminat- 
ing so far as possible differences in yield due to variability in the 
soil, are calculated by adding to the yield of the plat next in suc- 
cession after a given check plat one-third the difference between 
the yields of the check plats on either side if the yield of the second 
check plat is lower than that of the first. If the larger yield is pro- 
duced by the second check plat, then one-third the difference is 
subtracted. Two-thirds of the difference is added to or subtracted 
from the yield of the plat next in order. Each group of four plats, 
consisting of two plats receiving different treatments and the two 
check plats on either side, is treated independently. The corrected 
1 yields are then compared with the yields of the preceding check 
: plat. 
In all cases the largest yields were obtained from the early irri- 
gated plats. Compared with the check plats the omission of one 
irrigation on the “medium” plats resulted in significant decreases 
in yield. On the “late” plats large decreases followed the with- 
holding of water until late in the season. Comparing the yields of 
‘ the medium and late irrigated plats, which received the same number 
of irrigations, but beginning earlier, we find that the yields of 
the former are substantially larger. 
In 1918 the proportion of the tubers which were marketable was 
determined for each of the lots grown under the different condi- 
tions of irrigation. The results are shoAvn in Table 11. 
It was found that in the case of both of the varieties used for 
this experiment the largest percentages of marketable tubers were 
obtained from the plats which had received the early irrigations. 
In the Pearl the check plats were next in order while in the Rural 
New Yorker the per cent of marketable tubers on the check plats 
was slightly lower than that which was obtained from the late irri- 
gated plats tho the difference is small and possibly within the limits 
of error. It was observed during the process of digging that the 
TABLE 11 
Effect of Time of Starting Irrigation on Percentage of Marketable Tubers. 
Summary of the Two Series for 1918. 
PLATS VARIETY 
Pearl Rural New Y'orker 
Per Cent Per Cent 
Early . 
Checks 
Late . 
93.2 
91.7 
90.5 
95.2 
93.1 
94.0 
