130 AGRICULTURAL REPORT. 
these two reasons, when the fluid which fills a cell congeals, the cell is 
found distended beyond measure, without, however, bursting in the gen- 
erality of cases. The elastic membrane of vegetable tissue thus dis- 
tended loses its elasticity to such a degree that many days of repose are 
afterward necessary for it to regain its original dimensions after the 
melting of the ice. Now, when we carry frosted plants into a warm 
place, the ice which the cells contain being melted, the water will return 
to its primitive volume smaller than that of the ice; but the air which 
the freezing has disengaged will prevent the cellular membrane from 
returning to its first condition. We find, therefore, in the cells of plants 
which have been thawed the water and the air remaining separately, 
the one next to the other. This air is not long in producing an injurious 
influence on the chlorophyl, or green, of the leaves, and killing that 
part. Hoffmann compared the action of this gas in the ceils of the 
leaves to the rapid mortal effect of the presence of bubbles of air in the 
blood of animals. .The method of preserving the chlorophyl and the 
_ organic matters from the injurious influence of the air consists of allow- 
ing the penetration of cold or warm water into the cells at the same 
moment when the vesicles of gas, which are retained between the needles 
of ice, become free by the fusion of the water, and commence to unite; 
then, as long as this air does not form a stratum, lodged between the 
water and the walls of the cell, it cannot cause the decomposition of the 
chlorophyl. Being free it dissolves little by little in the liquid, or 
escapes gradually to the exterior by the vessels of the plant. 
When, rarely enough, frozen plants which are thawing very slowly to 
a temperature near that of melting ice escape death, it is because the 
disengagement of the air from the ice takes place very slowly and in 
such a manner that the vegetable membrane has time gradually to 
regain its original volume by its elasticity. 
To sustain this opinion on the cause of the death of plants by frost, 
Hoffmann reports a number of observations, from which it results that 
the leaves always diminish in volume when they freeze; in the jonquil, 
for instance, the leaves diminished in freezing 21 parts to 100, or nearly 
one-fourth. This diminution of volume is always recognizable at first 
sight, and is produced with such rapidity that it is the same after ten 
minutes of freezing as after ten to thirty hours. Hoffmann believes 
that it is due in part tothe fact that the air becomes free by the freezing 
of the cellular juices, and escapes from the leaves. 
But how can we reconcile this remarkable diminution of the frozen 
leaves with the fact that the cells increase in volume by the freezing of 
the water, and by the disengagement of the air contained in it? Hoff- 
mann believes that this increase is more than counterbalanced by the 
_ contraction of the epidermis, experienced through the entire leaf, (which 
thus becomes very tough and consistent,) and the presence of the air 
existing in the vessels and the intercellular spaces. The enlargement 
of the ceils operates interiorly altogether, and at the expense of the 
vessels and spaces which oppose less resistance than the enveloping 
epidermis. 
If, says Hoffmann, this explanation of the process which causes the 
death of frozen plants is really the true one, we may probably deduce 
from it the aptitude of certain plants for resisting the frosts. They 
appear to owe this property to the membrane of their cells, which pos- 
sesses an elasticity sufliciently energetic to enable them to resist the 
distension produced by the action of the frosts, and to recover their 
original dimensions as the ice again becomes water, in such a way that 
the disengaged air is forced to dissolve rapidly under the pressure exer- 
