SUMMARY 
1. Injury to seed corn by freezing in the fall is of fre- 
quent occurrence in Nebraska. The underlying causes of such 
injury are: (1) Late maturity, (2) abnormally early freezing 
weather. 
2. The embryo, which is the vital part of a corn kernel, is 
in reality a rudimentary corn plant, having small leaves, stalk, 
and root. 
3. In the normal process of germination, or growth of the 
embryo, the primary root develops more rapidly than the 
plumule. 
4. The embryo and endosperm of a kernel of corn develop 
approximately at the same rate from the time of fertilization 
until maturity, and the power of germination is attained in 
about 20 days after fertilization. 
5. The embryo and endosperm in an air-dry kernel of 
corn contain practically the same percentage of moisture. How- 
ever. during the period just before maturity the percentage is 
greater for the embryo. 
6. When immature or moist kernels of corn are sufficiently 
exnosed to freezing temperatures, ice is formed in the inter- 
cellular spaces and in the larger spaces around the scutellum, 
plumule, primary root, and root sheath. 
7. Severe freezing of immature or moist corn causes the 
embryo to change from a normally light or creamy color to a 
dark or yellowish brown color. This change is usually accom- 
panied by a loss of vitality. The appearance of the embryo, 
therefore, is a fairly safe guide in judging the germinative 
power of seed corn which has been subject to freezing injury. 
8. So far as could be detected from microscopic examina- 
tions of frozen embryonic tissues, there was no rupturing of 
cell walls or other cytological effect of freezing and ice forma- 
tion. The change in color of the embryo as a result of freezing 
would seem to indicate that a chemical change had taken place. 
9. The real cause of death from freezing of plant tissues 
is a difficult matter to determine. Nevertheless, several theories 
based on certain observations have been advanced to explain it. 
The most generally accepted theory is that water is withdrawn 
from the cells during the process of freezing, and that this 
process continues until death results from desiccation of the 
protoplasm. The most satisfactory explanation, however, in 
the light of the evidence at hand, is found in the theory, that 
freezing produces a physical or chemical change, aside from the 
withdrawing of water, in the protoplasmic and nuclear material 
of the cell so that the element of life no longer exists. 
