1 *OTATO I N VP^STIG ATION S 
19 
time that the seed had been grown at the station. On the other hand 
the Eiiral New Yorker showed an increase in yield up to and includ- 
ing the third year and a decrease the fourth year, tho it should be 
noted that -the yield of the 1915 seed was greater by 39.8 bushels 
per acre than that of the new seed. Whether the falling olf in yield 
from the three-year-old seed indicates that a permanent degener- 
ation has begun can be determined only by further experiments. The 
fact that the original stock from which this seed was obtained has 
been grown continuously in this locality without change of seed 
for approximately twenty years with no apparent signs of running 
out, suggests the improbability of any great deterioration in this 
variety so long as it can be kept free from certain diseases which 
tend to cause degeneration. 
While the time covered by these experiments is not sufficient 
to settle the matter conclusively there are some deductions that can 
be made. One point of significance is the different behavior of the 
two varieties,, which is readily explained. The Rural New Yorker 
plats showed very little evidence of disease, in fact this variety 
appears to be very nearly immune to the diseases which are con- 
sidered as being responsible for one form of degeneracy. On the 
other hand the Pearl variety, with the exception of the plats grown 
from the new seed, was badly affected with Mosaic disease which 
appeared to increase in intensity with the length of time that the 
seed stock had been grown at the station. Accompanying this con- 
dition was a gradual diminution of yield from year to year. A 
similar instance of running out due to a diseased condition of the 
plants was observed in the Peachblow grown in 1916 from one-year- 
old seed. It is believed that the greater part of the running out of 
varieties which has been observed by growers in the West is largely 
due to the effect of certain of the so-called nonparasitic diseases, 
including Mosaic, Leaf-roll and possibly others. These diseases at- 
tack the vines thereby reducing the vigor of the plants and ulti- 
mately the yield. The shape of the tubers is not necessarily affected 
so that the diseased condition may not be apparent in the cellar 
tho in the advanced stages rough, elongated types are frequently 
found. 
There is another type of running out which is occasionally found 
in individual hills which appears to be more strictly a physiological 
degeneration. In this case the condition is usually one of excessive 
vine growth which is apparently not associated with any disease, a 
heavy production of seed balls and with tubers of abnormal shape 
