Effects of Frost on Plants. | 25 
thousand pieces in the Horticultural Society’s Garden, and a few 
cases are cited in which the bark and trunk of trees was rent. - 
“The expulsion of air from aeriferous organs, and the introdue- 
tion of it into parts not intended to contain it, isa striking phenom- 
enon. Every one must have remarked that when a leaf has been 
frozen to death, it changes color as soon as thawed, acquiring a 
deeper green, and being nearly of the same depth of color on both 
sides; the same appearance is produced by placing a leaf under the 
exhausted receiver of an air-pump, and in both cases is owing to the 
abstraction of air from the myriads of little air-chambers contained 
in the substance of this organ. If the leaf of Hibiscus Rosa-Si- 
nensis, in its natural state is examined, by tearing off the paren- 
chyma from the epidermis with violence, it will be found that the © 
sphincter of its stomates, the cells of the epidermis, and the cham- 
bers immediately below the latter, are all distended with air; but 
in the frozen leaf of this plant the air has entirely disappeared, the 
sphincter of the stomates is empty ; the upper and under sides of 
the cells of the epidermis have collapsed and touch each other, 
and all the cavernous parenchyma below the epidermis is transpa- 
- rent, as if filled with fluid. Whither the air is conveyed is not 
apparent; but as the stomates have evidently lost their excitabil- 
ity, and are in many cases open, it may be supposed that a part of 
the air at least has been expelled from the leaf; and as the pith 
of this plant in its natural state, contains very little air, and in the 
frozen state is found to be distended with air, it is also probable 
that a part of the gaseous matter expelled from the leaf when 
frozen is driven through the petiole into the pith. In the petiole 
of tsi pant. are numerous annular and reticulated vessels, which ~ 
under are filled with air, but after freezing 
are found: d filled with fluid ; is it not possible that their functions 
may have been disturbed “by the violent forcing of air through 
them into the pith, and that when that action ceased, they were 
incapable of recovering from the overstrain, and filled with fluid 
filtering through their sides? ‘That annular ducts are in some 
way affected by frost, was shown by their state in a thawed 
branch of Euphorbia 'Tirucalli, when they were found in a collaps- 
ed state, empty of both air and fluid, with their sides shrivelled, 
and with the fibre itself, which forms the rings, also wrinkled trans- 
versely. The minute long-haired leaves of Erica sulphurea are 
in their natural state firm, bright green, with a rigid petiole, and 
Vol. xxx1x, No. 1—April-June, 1840. 4 
