88 BOTANY. 
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. (82° 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 slots in the 
spring are often killed by slight frosts. 
180. Death from low temperature is always accompanied 
by the formation of ice-erystals 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 
