88 BOTANt. 



tissues chemical changes at once begin, resulting in the 

 rapid disintegration and decay of the substances in the 

 cells. 



178. In many respects the results of too great a reduc- 

 tion of temperature are similar" to those produced by too 

 great an elevation. There is observed the same coagula- 

 tion of the albuminoids, resulting in the destruction of the 

 power of the protoplasm to imbibe water, and, as a conse- 

 quence, in the loss of the turgidity of the cells. More- 

 over, as in the case of injury from high temperature, those 

 cells which are the most watery are the ones which, other 

 things being equal, are injured most quickly by a reduc- 

 tion of temperature. 



179. Embryo plants in seeds, when dry, are able to endure 

 almost any degree of low temperature; but after they have 

 germinated, and the cells have become watery, they are 

 generally killed by a reduction to, or a few degrees below, 

 0° Cent. (32° Fahr.). So, too, the comparatively dry tissues 

 of the winter buds and ripened stems of the native trees 

 and shrubs in cold countries are rarely injured even in the 

 severest winters, while the young leaves and shoots in the 

 spring are often killed by slight frosts. 



180. Death from low temperature is always accompanied 

 by the formation of ice-crystals in the succulent tissues; 

 these are formed from the water of the plant, which is 

 abstracted from it in the process of congelation. Much of 

 the water thus frozen is that which fills the cavities (vacu- 

 oles) of the cells, while some of it is that which moistens 

 the protoplasm and cell-walls. 



181. As the liquid in the vacuoles is not pure water, but 

 a mixture of several solutions, it freezes at a lower tem- 

 perature than water, and then, according to a well-known 



