Transactions of the London Horticultural Society. 509 



table 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 V 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 ve- 

 getable tissue, undergo any alteration, unless perhaps in the case of amyla- 

 ceous 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 dilatation thus produced not being 

 sufficient to burst the sides of the cavities. 4. That such dilatation is prin- 

 cipally 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 phaenomena attendant upon freezing : introducing gaseous 

 matter into organs not intended to elaborate it, and bringing about the first 

 stage in a 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 tlie 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 a 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 con- 

 tinuous mass, but that it is a collection of a multitude of little microscopical 

 icicles. Under the microscope the fact becomes evident. We know how 

 excessively hard some fruits become when frozen by this mosaic of icicles, es- 

 pecially pears. If we thaw them, it is seen that on the instant a multitude of 

 air-bubbles are extricated from the juice of the fruit, and that this juice has 

 then acquired new chemical qualities. I wished to ascertain the cause of these 

 phgenomena, and the following is what 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 

 from 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 crys- 

 tals, as may be seen by freezing water in a cylindrical vessel, when the air- 

 bubbles always assume the form of a very long cone, terminated by a spherical 

 cap. The augmentation of the volume of water is in 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 be- 

 comes individually larger. When thawed, the cell recovers itself by the elas/- 



L L 3 



