"I could not find the vesicles of cellular tissues separable from each other, even in the most succulent species submitted to experiment, and I conclde that this circumstance, to which Professor Morren attaches importance, and to which M. Payen ascribes the difficulty of extracting starch from frozen potatoes, is not so much connected with the destruction of vegetable life, as a result produced upon the tissue by a great intensity of cold. I did, however, find it lacerated in several cases, as if by the distension of the fluid it had contained. In a Stapelia the whole of the cellular tissue was soft, and deformed, as if it had been extended, with but little power of recovering itself again, and several large irregular lacerated cavities were observed. The same appearances were remarked in Euphorbia Ti rucalli, but the laceration of the tissue was much less extensive. In Hibiscus Rosa Sinensis the cells of the cortical integument, (mesopbloeum,) were very much torn, and in Hibiscus milltaris, not only the cells of the bark, but especially those of the pith, were so completely broken up, that it was difficult to obtain a thin slice of those parts for examination. In no case, however, have I found any kind of tissue ruptured, except the soft cellular dodecahedral or prismatical.

It would also seem that M. Payen recognizes the laceration of tissue by frost, for he ascribes the acridity of frozen potatoes to an extravasation of the acrid matter which exists in the epiphlceum of such tubers,- and which, in a natural state, is locked up in the cells of which that part consists. Independently of these observations, it is not to be doubted that frost does split the tissue of plants. I saw the youngest shoots of Erica mediterranea, cinerea, and others, shivered into thousands of pieces in the Horticultural Society's Garden, on the morning of the 20th of January. The branches of the Melaleucas were rent to their points at Carclew. Several cases, among others that of the common holly, were observed at Claremont, where the bark was split and rent asunder from the wood below it; and Sir Oswald Mosley has given me the following 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 different places, to the height of thirteen feet three inches.

There was an interval of eleven inches between the two shakes, whieh were each of them 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 aeriferous organs, and the introduction of it into parts not intended to contain it, is a striking phenomenon. Every or.e 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 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 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 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 transparent, as if filled with fluid.

Whither the air is conveyed is not apparent; but as the stomates have evidently lost their excitability, 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 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 fonns the rings, also wrinkled transversely. Facts of an analogous kind were remarked by me in Erica sulphnrea.

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 compresaorium, at first offer perceptible resistance to its action, and afterwards, as the pressure increases, discharge, chiefly through their petiole, a great quantity of air. But leaves of this plant, which have been frozen by exposure to the ternperature 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 comparatively 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 pressure having been exercised upon them.