" In considering the various circumstances alluded to in this paper, I was naturally led to inquire into the exact manner, in which the death of plants is caused by cold. Very little, however, is to be learned upon this subject from the writings of physiologists.

" The common opinion is, that frost acts mechanically upon the tissue of plants, by expanding the fluid they contain, and bursting the cells or vessels in which it is enclosed.

" M. Goeppert, of Breslau, in a paper originally read at the meeting of German naturalists, at Leipsig, in 1829, briefly abstracted in Oken's Isis for 1830, p. 497, and translated in the Edinburgh Journal of Natural and Geological Science for 1831, p: 180, denies that this supposed laceration of vegetable tissue by frost, takes place. He is represented to have stated, that the changes which plants undergo, when they are killed by cold, do not consist in a bursting of their vessels or cells, but solely in an extinction of vitality, which is followed by changes in the chemical composition of their juices.

"Professor Morren, of Liege, in a paper printed in the fifth volume of the Bulletin de l' Academic Royale de Bruxelles, has published some exceedingly interesting observations upon this subject. Like M. Goeppert, he denies the truth of the statement generally made, that frost produces death in plants by bursting their vessels; and he assigns the effect to other causes. His more important conclusions are, 1. That no organ, whatever, is torn by the action of frost, except in very rare cases, when the vesicles of cellular tissue give way, but that the vesicles of plants are separated from each other by frost, without laceration. 2. That neither the chlorophyll, the nucleus of cells, elementary fibre, amylaceous matter, raphides, nor the various crystals contained in vegetable tissue, undergo any alteration, unless, perhaps, in the case of amylaceous matter, which, in some cases, is converted into sugar, no doubt, in consequence of the action of some-acid, formed by the decomposition of the organic parts. 3. That the action of frost operates separately upon each individual elementary organ, so that a frozen plant contains as many icicles as there are cavities containing fluid; the dilitation thus produced not being sufficient to burst the sides of the cavities. 4. That such dilitation is principally owing to the separation of the air contained in the water. 5. That this disengagement Of air by water, during the act of congelation, is the most injurious of all the phenomena attendant upon freezing: introducing gaseous matter into the organs not intended to elaborate it, and bringing about the first stage in the decomposition of the sap and the matters it precipitates; so that with a thaw commences a new chemical action, destructive of vegetable life. 6. That the expansion of the cells, and aquiferous organs, drives a great quantity of water into the air-cells and air-vessels, so that the apparatus intended to contain liquid only, contains water and air, while that which is naturally a vehicle for air, conveys water.

Such an inversion of functions must necessarily be destructive to vegetable life; even if death were not produced in frozen plants by the decomposition of their juices, the loss of their excitability, and the chemical disturbance of all their contents.

"Professor Morren's observations were made upon various plants frozen in the spring of the present year, having been exposed to ft temperature of - 4° to +9° Fahrenheit. One of his statements I give in his own words. ' In the parenchyma of many plants, and especially in that of succulent fruits, it is easy to ascertain what modifications are caused by frost in the internal organs of plants. If a frozen apple is opened, it is obvious that the ice is not a continuous mass, but that it is a collection of a multitude of little microscopical icicles. Under the microscope the met becomes evident. We know how excessively hard some fruits become when frozen by this mosaic of icicles, especially pears. If we thaw them, it is seen that on the instant a multitude of air-bobbles are extricated from the juice of the fruit, and that this juke has then acquired new chemical qualities. I' wished to ascertain the cause of these phenomena, and the following is whet observation has shown me. I studied for this purpose, more particularly the tissue of the apple. Each cell is filled with a small icicle, which has in its middle a bubble of air.

We know that when water freezes, the crystals so arrange themselves, that the air separated frem their mass by the solidification of the liquid is intercalated between their planes. This air also places itself in a mass of congealed water in a regular manner, the nature of which depends entirely upon that assumed by the crystals, as may be seen by freezing water in a cylindrical vessel, when the air-bubbles always assume the form of a very long eone, terminated by a spherical cap. The augmentation of the volume of water is in a great measure owing to this interposition of masses of air. All these effects take place in each , cell of a frozen apple, which thus increases in size because each cell of its tissue becomes individually larger. When thawed, the cell recovers itself by the elasticity of its vegetable membrane, and frozen fruit becomes, as we know, very much shriveled. Each cell, therefore, acts like a bottle of frozen water, only there is no bursting, because the membrane is extensible.'

" But when plants easily killed by cold, are exposed to so low a temperature as that just described, it is to be feared that phenomena actually connected with the destruction of vegetable life, may be intermixed with others, which merely indicate the physical effects of cold upon vegetable matter already dead. For the purpose of judging how far this conjecture is well founded, I have carefully examined the pott mortem appearances of several plants kilted by exposure to a temperature artificially reduced only to from 28° to 30° Fahrenheit. These observations, while they have confirmed the general accuracy of Professor Morren's statements, have led to other conclusions which also appear important.