THE MOLECULAR FORCES IN PLANTS. 123 



2 See Detmer, Lehrbuch d. Pflanzenphysiologie, 1883, p. 151. 



3 See Loew and Bokorny, Die cliemische Ursache des Lebens, and Botan. 

 Zeitung, 1882, p. 824. 



4 See Schimper, Botan. Zeitung, 1880, No. 52. 



II. DISORGANISATION OF THE MOLECULAR STRUC- 

 TURE. 



47. The Influence of Low Temperatures on Plants. 



Plants behave very differently under the influence of low tem- 

 peratures. Many plants (many lichens, mosses and bacteria, but 

 also higher plants, e.g. Bellis perennis and Stellaria media, etc.) 

 keep alive when frozen at a temperature of from 6 to 8 C., 

 and then quickly thawed. I placed leaves of Primula elatior in 

 winter in glasses, which were closed and then surrounded by a 

 freezing mixture consisting of snow and common salt. The leaves 

 remained for six hours exposed to a temperature of 5 to 8 

 C., and were then quickly thawed by immersion in water at a 

 temperature of 6 C. At the close of the experiment, the leaves 

 were still living. 



If we expose potatoes in the open, or in glass vessels surrounded 

 by a freezing mixture, to a temperature of 8 C., they freeze 

 through and through, and become ringing hard. Leaves, e.g. 

 leaves of the Crassulaceas, or of the cabbage, rape, or bean, 

 when exposed to a temperature of 8 C., freeze, and become as 

 brittle as glass. If we thaw the frozen potatoes or leaves by 

 placing them in water, they perish. They have frozen to death, 

 and now exhibit the characteristics to be described in 48. 



I have fully satisfied myself by repeated experiments that 

 potatoes whose tissues have been really frozen, always prove, after 

 thawing, to be dead, whether they are thawed slowly or quickly. 

 We place a few potatoes in water in a large vessel, and expose 

 this to a temperature of 8 C., so that the potatoes slowly 

 freeze. The ice and the potatoes can then be very slowly thawed 

 by placing the vessel in a place kept at a temperature of +1 

 h'2 C. The thawed tubers are dead. I obtained the same 

 result with leaves of Escheveria. I have also experimented with 

 plants of Zannichellia palustris, which, when lying in water, 

 exposed to the light, gave off large quanties of Oxygen. After 



