26 Effects of Frost on Plants. 



upon being exposed to pressure in a compressorium, offer at first 

 perceptible resistance to its action, and afterwards, as the pressure 

 increases, discharge, chiefly through their petiole, a great quan- 

 tity of air. Bat tlie leaves of this plant which have been frozen 

 by exposure to the temperature 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 compara- 

 tively 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 pres- 

 sure having been exercised upon them. I am inclined to refer 

 to this cause the well known fact, of which many cases have oc- 

 curred this winter, that the sudden exposure of frozen plants to 

 warmth will kill them ; though they may not sufier if warmed 

 gradually. In such cases, it may be supposed that the air, forced 

 into parts not intended to contain it, is expanded violently, and 

 thus increases the disturbance already produced by its expulsion 

 from the proper air-cavities; while on the other hand, when the 

 thaw is gradual, the air may retreat by degrees from its new situa- 

 tion without producing additional derangement of the tissue." 



The action of frost upon the chlorophyll, or green coloring mat- 

 ter of leaves, is next noticed ; and also upon the amylaceous mat- 

 ter, or starch, which is so abundant in many plants. This last is 

 always found to be diminished after freezing, and more or less 

 altered ; and in the well known case of the potatoe, the starch 

 which has disappeared is supposed to have furnished the sugar 

 formed in the process of freezing this tuber. 



. " Finally, it appears that frost exercises a specific action upon the 

 latex, destroying its power of motion. If, as Prof Schultz sup- 

 poses, this is the vital fluid of plants, such a fact would alone ac- 

 count for the fatal effects of a low temperature. In all the cases 

 I have observed frost coagulates this fluid, collecting it into amor- 

 phous masses. 



"In Stapelia, where the laticiferous vessels are easily found, the 

 latex itself is so transparent, that it is difficult to perceive it in a 

 living state, even with the best glasses ; but after freezing it is 

 distinctly visible, resembling half coagulated water. In the Hi- 

 biscus above mentioned, the stem is covered with long and rigid 

 simple hairSj filled with a plexus of laticiferous vessels of extreme 



