22 Nebraska Agricultural Exp. Station Research Bul. 16 
ject to injury from ice formation. Wiegand (1906) found the 
upper and lower parts of leaves entirely separated by layers of 
ice, and also the outer layers of twigs separated from the inner 
by a sheet of ice. The injury resulting from the freezing of 
green plants is due to the change in volume when the water in 
the plant freezes, according to Gassner and Grimme (1913), 
and not to any special effect upon the plant cells. The result 
of this increase in volume is a tearing of the tissues, or a break- 
ing up of the cell structure. This form of injury is recognized 
by Chandler (1913) as being entirely possible, for he speaks of 
the tearing of tissues due to the tension developed at low 
temperatures, 
While studying the influence of the temperature of liquid 
hydrogen on the germinative power of seeds, Thiselton-Dyer 
(1899) suggest that the sudden vacuum caused within the seeds 
by immersing them in liquid hydrogen might possibly produce 
physical ruptures which would weaken or destroy their vitality. 
Adams (1905) also mentions the possibility of injury from this 
source, but thinks the vacuum too small to be of any serious 
consequence. He concludes, further, that the intercellular spaces 
in seeds are very small, and that in moist seeds, after freezing 
has gone on for some time, these spaces become filled with a 
solid mass of ice. Then if the temperature is still further low- 
ered, more ice is formed, and it is likely that complete rupture 
takes place, causing a separation of the cells from each other. 
TOO RAPID THAWING 
Many have thought that the phenomenon of death from 
freezing is not due directly to freezing but to the rate or 
rapidity of thawing. Sachs (I860) an early investigator, was 
an ardent supporter of this belief, and for many years his work 
was considered conclusive. Eater, Muller-Thurgau (1886) 
pointed out inaccuracies in his work and showed by experiments 
with a large number of plants that there was no difference in 
the amount of killing whether tissues were thawed rapidly or 
slowly, except in the case of ripe apples and pears. It was 
found also bv Mol i sell (1897) and Chandler (1913) that in 
general the rate of the wing is not related to the amount of kill- 
ing at a given temperature, the exceptions to this rule being 
the loaves of lettuce, leaves of Agave amerieana, and ripe apples 
and pears. In arguing against the theory that plant tissues 
are killed by the rate of thawing rather than by freezing, 
Detmer ( 189*3) mentions several mosses which can remain in a 
hard frozen condition for a long time without showing any 
