24 Effects of Frost on Plants. 



certain the cause of these phenomena, and the following is what 

 observation has shown me. I studied for this purpose more par- 

 ticularly 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 alsa 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-bub- 

 bles 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 becomes individu- 

 ally larger. When thawed the cell recovers itself by the elasticity 

 of its vegetable membrane, and frozen fruit becomes, as we know, 

 very much shrivelled. 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 veget- 

 able life may be intermixed with others, which merely indicate the 

 principal 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 post mortem appearances of several 

 plants killed 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 state- 

 ments, have led to other conclusions, which also appear impor- 

 tant." In these cases Dr. Lindley remarks that he did not find 

 the vesicles of cellular tissue, separable from each other, even in 

 the most succulent species, whence he concludes that this result 

 is not essentially connected with the destruction of vegetable life, 

 but is the effect of a great intensity of cold upon the tissue. In 

 several instances, however, he found the tissue lacerated, as if by 

 the distension of the fluid it had contained ; and sometimes he 

 found the cells so completely broken up, that it was difficult to 

 obtain a thin slice for examination. The young shoots of several 

 species of Erica, and of some other plants, were shivered into a 



