90 LIVING PLANTvS 



been driven out of the cell sap, protoplasm 

 and wall, and may be seen piled up in the 

 spaces in the form of small pillars or discs, in 

 many instances completely fillingup the space 

 between the cells and forcing them apart, 

 but not injuring the protoplasm or the cell 

 wall by the crystallization of water in their 

 interstices. It is thus to be seen that the ex- 

 trusion of water into the intercellular spaces 

 is a protective device of the protoplasm. In 

 many instances the amount of ice formed in 

 the spaces among the cells may be so great as 

 to split the tissues completely apart. This is 

 especially noticeable in trees, and the sudden 

 yielding of the firm wood to the pressure of 

 the ice crystals within is accompanied by 

 startling reports familiar to those who fre- 

 quent the forests in the early days of winter. 

 In manj' of the herbaceous plants the split- 

 ting of the stems is followed by the formation 

 of very delicate and fantastically arranged 

 sheets of ice crystals, which are commonly 

 known as "frost flowers." 



The excretive power of protoplasm is not 

 always sufficient to enable it to reduce the 

 percentage of water in the cell to such a degree 

 as to escape freezing. In such instances, ice is 

 formed inside the cell, and the withdrawal of 

 practically all of the water in the protoplasm 

 to form the crvstals results in the architec- 



