DESTRUCTION OF PLANTS BY FROST. 



others that of the common holly, were observed at Claremont, where the bark was split 

 and rent asunder from the wood below itj and Sir Oswald Mosley has given me the fol- 

 lowing instance, which occurred under his own observation. ' An oak tree, growing upon 

 the south side of a hill, in a sheltered situation, in Knightly Park, near Burton-upon- 

 Trent, in the county of Stafford, was rent in the severe frost of last winter in two diffe- 

 rent places, to the height of thirteen feet three inches. There was an interval of eleven 

 inches between the two shakes, which were each of therti one-quarter of an inch wide, and 

 extended in depth to the heart of the tree. The girth of the tree is six feet ten inches, 

 and as soon as the frost went the openings closed again, and the tree is now as flourishing 

 as ever.' To these cases many more might be added. 



"The organization of woody tissue appears to be affected, but not by laceration. If a 

 frozen and unfrozen transverse slice of the stem of Hibiscus Rosa Sinensis be placed, side 

 by side, upon the field of the microscope, it is obvious that the diameter of the tubes of 

 the wood and liber, is considerably less in the former than in the latter; this appears to 

 be owing to an increase in the thickness of the sides of the tubes, which has the effect of 

 diminishing their calibre. 



" The expulsion of air from feriferous organs, and the introduction of it into parts not 

 intended to contain it, is a striking phenomenon. 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 of nearly the same depth of color on both sides; the same ap- 

 pearance 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 Sinensis in its natural 

 state is examined, by tearing off the parenchyma from the epidermis with violence, it will 

 be found that the sphincter of its stomates, the cells of the epidermis, and the chambers 

 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 up- 

 per and under sides of the cells of the epidermis have collapsed, and touch each other, and 

 all the cavernous parenchyma below the epidermis is transparent, as if filled with fluid. 

 Whither the air is convej^ed is not apparent; but as the stomates have evidently lost their 

 excitability, and are in many cases open, it may be supposed that apart of the air at least 

 has been expelled from the leaf; and as the pith of this plant, in its natural state, con- 

 tains 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 this plant are numerous annular and 

 reticulated vessels, which, under ordinary circumstances, are filled with air, but after 

 freezing are found 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 collapsed state, empty of both air and fluid, with their sides shrivelled, and with the 

 fibre itself, which forms the rings, also wrinkled transversely. Facts of an analogous 

 kind were remarked by me in Erica sulpliurea. The minute long-haired leaves of this 

 species are in their natural state firm, bright green, with a rigid petiole, and upon being 

 exposed to pressure in a comprcssorium, at first offer perceptible resistance to its action, 

 fterwards, as tlie pressure increases, discharge, chiefly through their petiole, 

 tity of air. But leaves of this plant, which have been frozen by exposure to the 



