26 Liffects of Frost on Planis. 
upon being exposed to pressure in a compressorium, offer at first 
perceptible resistance to its action, and afterwards, as the pressure 
increases, discharge, chiefly through their petiole, a great quan- 
tity of air. But the leaves of this plant which have been frozen 
by exposure to the temperature of 27° are very different ; they 
are softer, dull olive-green, with a flaccid petiole, and offer but 
little resistance to pressure ; yet, although they give way freely, 
the quantity of air which the compressorium expels is compara- 
tively small, and readily driven out. Moreover, the long hairs of 
this plant, which in the natural state are occupied by fluid, were 
always found filled with air after freezing, and this without pres- 
sure having been exercised upon them. Iam inclined to refer 
to this cause the well known fact, of which many cases have oc- 
curred this winter, that the sudden exposure of frozen plants to 
warmth will kill them; though they may not suffer if warmed 
gradually. In such cases, it may be supposed that the air, forced 
into parts not intended to contain it, is expanded violently, and 
thus increases the disturbance already produced by its expulsion 
from the proper air-cavities; while on the other hand, when the 
thaw is gradual, the air may retreat by degrees from its new situa- 
tion without producing additional derangement of the tissue.” 
The action of frost upon the chlorophyll, or green coloring mat- 
ter of leaves, is next noticed ; and also upon the amylaceous mat- 
ter, or starch, which is so abundant in many plants. This last is 
always found to be diminished after freezing, and more or less 
altered ; and in the well known case of the potatoe, the starch 
which has disappeared is supposed to have’ furnished the sugar 
formed in the process of freezing this tuber. 
“Finally, it appears that frost exercises a specific action upon the 
latex, destroying its power of motion. If, as Prof. Schultz sup= 
poses, this is the vital fluid of plants, such a fact would alone ac- 
count for the fatal effects of a low temperature. In all the cases 
I have observed frost coagulates this fluid, collecting it into amor- 
phous masses. 
“In Stapelia, where the laticiferous vessels are easily found, the 
latex itself is so transparent, that it is difficult to perceive it ina 
living state, even-with the best glasses; but after freezing it is 
distinctly visible, resembling half coagulated water. In the Hi- 
discus above mentioned, the stem is covered with long and rigid 
simple hairs, filled with a plexus of laticiferous vessels of extreme 
