72 Nebraska Agricultural Exp. Station Research Bul. 16 
six, and three per cent of the corn in the respective cribs were 
selected for the above grades. 
THE DANGER LINE OF FREEZING INJURY 
An approximate safety zone free from freezing injury may 
be established for seed corn differing in moisture content. The 
combinations of low temperature and freezing duration which 
seed corn will withstand as indicated in Fig. 13, are constructed 
from the various tests reported in this bulletin and should be 
regarded as approximate rather than absolute. They set forth 
the probable duration of a given low temperature which corn 
of given moisture content Avill withstand without injury. A 
slight lowering of the temperature or a longer duration of the 
exposure may initiate a reduction in the per cent germination 
but will not prove entirely fatal. Greater fatalitv will result 
as the adverse factors are extended. 
It will be noted that in general an extension of the time of 
exposure is comparatively as dangerous as is the lowering of 
the temperature, until the moisture content in the grain is 
reduced to nearly 20 per cent where it manifests a decidedly 
greater resistance to the duration of exposure. A still more 
marked proportional resistance to the duration of exposure is 
shown by corn containing as low as 17 per cent moisture. When 
air-dry, containing 1-1 per cent or less of moisture, corn will 
endure any natural low winter temperature for any length of 
time. 
OCCURRENCE OF AUTUMN FROSTS IN NEBRASKA 
The dates for the first autumn frosts occur with great 
irregularity in Nebraska. As extremes for Lincoln. Xebr., dur- 
ing the last 21 years, the first killing frost occurred in 1902 on 
September 12, and in 1914 on October 27. As seen in Table 31 
the dates of the first killing frost and the first dates with a record- 
ed freezing temperature of 32° F. or lower do not always coincide. 
This is due to the fact that the Weather Bureau temperatures 
are obtained at a considerable distance above the ground, where 
the temperature does not always drop quite so low as it does 
nearer tin* surface. The average date of the first killing frost 
at Lincoln during the past 21 years has been October 12. 
Table 31 gives tin* duration of the first freezing temperature 
together with the mean and minimum temperatures of the 
period, during the last 21 years at Lincoln. 
