226 CHEMISTRY OF PLANT LIFE 



water contributes greatly to the possibilities of the chemical 

 reactions which constitute life processes. 



Water, likewise, has a higher dialectric constant than any other 

 common liquid. This means that it does not readily conduct 

 electricity, or readily permit electric equilibrium to be established 

 in it; or, in other words, that it is a good insulator. This prop- 

 erty permits the existence in it simultaneously of materials having 

 opposite electric charges, or the so-called ionization phenomena; 

 hence, water is the best-known ionizing medium, and ionization 

 favors chemical reactivity. 



Again, water has a very high specific heat, a fact which is of 

 the utmost biological importance. It takes more heat to raise the 

 temperature of one gram of water through one degree than is 

 required to produce the same result in any other known sub- 

 stance; or, stated the other way around, a given amount of heat 

 will cause less change in temperature of water than of any other 

 known substance. Further, the latent heat of liquefaction and of 

 vaporization (i.e., the amount of heat required to change the sub- 

 stance from solid to liquid and from liquid to gaseous state, 

 respectively) is greater for water than for any other common sub- 

 stance. These facts are of very great importance in cell-proto- 

 plasm. The high specific heat of water provides that the heat 

 liberated by the chemical reactions which take place in the proto- 

 plasm can be absorbed by the water of the cell contents, and given 

 off again to other reactions, with very slight effect upon the tem- 

 perature of the protoplasm itself. Hence, violent changes in 

 temperature, which might be disastrous to the life of the cell, are 

 prevented by the high specific heat of the water which it contains. 

 Similarly, the high latent heat of liquefaction of water, resulting 

 in the giving up of large quantities of heat before it can become 

 solid, or " freeze," tends to prevent freezing and thawing of the 

 cell contents with sudden changes of external temperatures at or 

 near the freezing temperature of water. 



As a result of its physical properties, as just briefly described, 

 water accelerates all kinds of chemical reactions in protoplasm, 

 both by solution and by ionization of such substances as undergo 

 electric dissociation; and serves to regulate the temperature of the 

 protoplasmic mass. Furthermore, in organic tissues, most of the 

 important chemical reactions of the protoplasm are reversible 

 hydrolyses; i.e., water actually enters into the reaction or is lib- 



