EFFECTS OF COLD 89 



water in a solution and water in capillary 

 spaces, or water of imbibition will not freeze 

 until the temperature falls a certain amount 

 below the freezing point ; and it will be perti- 

 nent to state at this point that the tempera- 

 ture of small plant bodies is approximately 

 the same as the surrounding air, with the ex- 

 ception of the flowers of certain aroids and 

 other plants. Ice then may not be formed 

 until the temperature of a plant has fallen 

 more or less below the freezing point, amount- 

 ing to two or even six degrees below in some 

 instances. The exact point will vary with the 

 specific constitution of the plant, as it does 

 in solutions of different substances. 



Protoplasm even in its simplest forms is 

 highly automatic, and self-regulating. When 

 the cells of a leaf are subjected to a low tem- 

 perature, they contract and a portion of the Relation of 

 water contained is driven out into the inter- the cell to cold 

 cellular spaces where it is frozen. By this pro- 

 vision the proportion of the water in the. cells 

 is reduced and the danger of ice formation 

 and consequent destruction is averted. If 

 now the temperature is again lowered an ad- 

 ditional amount of water is forced into the 

 intercellular spaces, rendering the cell solu- 

 tions still more concentrated, and less easily 

 crystallized into ice. This process may con- 

 tinue until the greater part of the water has 



