Degree Type


Date of Award


Degree Name

Doctor of Philosophy



First Advisor

Joseph S. Burris


Ice nucleation in seed of maturing seed corn (Zea mays L.) was not influenced by the attachment or detachment of leaves or the stalk. Nucleation was influenced by the absence or presence of the husk. When the husk was removed from the ear, nucleation occurred at lower temperatures so greater damage resulted. The husk appeared to be the site of initial nucleation for the ear. Single seeds supercooled 2 to 3 C lower than seeds attached to the ear;Nucleation of seeds still attached to the ear gave the appearance of randomness. This may have been due to the heat released when the water changed state in the individual seed. The heat was partially passed to adjacent kernels, especially those in the same row because of their larger surface area contact;Nucleation occurring in single seed at -6 C required an additional exposure of only 15 to 30 minutes for the seed to be injured. It was not possible to injure seed at -3 C in the growth chamber even though seed in field experiments were damaged at -2 C;Measurement of the electrical conductivity of soaking water from fresh seed exposed to a frost may be useful in determining damage. Correlations were determined between conductivities from various soak periods and germination. Standard deviations of the individual seed conductivities were also checked for correlation with germination. The conductivity means were more highly correlated with germination than the conductivity standard deviations. The 4 and 8 hour soak periods had the highest correlation with germination. The 8 hour soak period was selected for damage assessment because it gave greater differences in conductivity for a change in germination;In 3 of 4 harvests of B73 over 2 years, any difference in germination was reflected by differences in conductivity after 8 hours of soaking. Carbohydrates were measured in the soaking water and found to be highly correlated with conductivity.



Digital Repository @ Iowa State University,

Copyright Owner

Verlyn Gerhard Fick



Proquest ID


File Format


File Size

144 pages