EFFECTS OF COLD 93 



temperature of three or four degrees above 

 freezing point for a single night. In such in- 

 stances the death of the leaves is due to the 

 fact that the chilling of the roots decreases 

 their ability to absorb water from the soil as 

 fast as it is needed by the leaves, v^hich shrivel, 

 blacken and dry up in consequence. If one of 

 these plants is placed in a pot and the earth 

 about the roots not allowed to approach 

 within fourteen degrees of the freezing point, 

 the shoot and leaves may be exposed to air 

 near the freezing point without injury. As has 

 been shown elsewhere the casting of autumn 

 leaves is a provision of deciduous plants, 

 whereby the leaves are cut away at the time 

 when the absorbing capacity of the roots 

 and the water supply is decreased. 



The power of excretion of water from the 

 cells by protoplasm is the primary means of 

 protection against death by cold, and is pos- Adaptations 

 sessed by all plant protoplasm. It is evident, ^2^^^* ^^ 

 however, that this is a method designed pri- 

 marily for the safety of each individual cell. 

 The organism as a whole may be expected to 

 exhibit adaptations to shield the cells from 

 the extremes of low temperature. The most 

 common device for escaping cold consists of a 

 deeply penetrating root system and the devel- 

 opment of underground stems. The roots are 

 sent down to a depth at which the tempera- 



