WINTER INJURY 265 



235. Sap concentration. — The work of Chandler on the 

 relation of sap concentration to the freezing of plant tissue is 

 particularly important. The experiments of Miiller-Thur- 

 gau and Molisch had previously shown conclusively that 

 practically all the formation of ice ciystals takes place in 

 the intercellular spaces and only rarely (due to very rapid 

 freezing) in the cells themselves. Furthermore, if the proto- 

 plasm or membrane surrounding it fails to give up its Avater, 

 the freezing point is thereby lowered or, in other words, a 

 protection is afforded. They also observed that tissue could 

 be super-cooled, just as a liquid, to a lower temperature than 

 that at which ice would normally form in the intercellular 

 spaces, and be raised again without ice formation and hence 

 without injuiy. 



Chandler has shown that if the sap concentration could be 

 doubled it would inhibit the loss of water, for twice as much 

 would l)e held in the protoplasm "at any given temperature 

 below the freezing point, but above the eutectic point ^ of 

 the solute," as a protection against freezing. Extensive 

 experiments were conducted with various kinds of herba- 

 ceous and woody plants and their fruits and leaves to de- 

 termine whether lowering their sap concentration would 

 lower their freezing point. The sap concentration was low- 

 ered by placing the plants in or by watering with solutions 

 of various salts, sugars, or glycerine. The freezing point of 

 the sap was then determined and reported in the terms of 

 "depression," which means "the number of degrees centi- 

 grade below zero at which, with no supercooling, ice forma- 

 tion begins in the sap." 



The following table (after Chandler) illustrates how uni- 



i"By the eutectic point is meant the temperature at which the 

 substance in soUition crystallizes out. At that temperature there 

 would be at the same time ice, crystals of solute, and unfrozen 

 solutions," 



