124 



tlie t'r(H'zini>- ])()iii1, particularly in living- lissuos. This sub- 

 ject will be discussed later in the section on Freezhig 

 Curves. 



The Double Freezing I * o i n t of Living 

 Tissues, Maximov (1914) described a very ])articular 

 course in the freezing curve of the living tissue of the 

 petiole of TussUago farfara. After subcooling, the tem- 

 l)erature rose rai)idly, then it sank a little and either stayed 

 at that level or rose again slightly (r/. Curves 1 and 2. 

 Fig. 7). There were apparently two freezing points 

 marked by two maxima on the curve. This author ob- 

 served furthermore that only the living tissues presented 

 the double freezing point, and that soaking the material in 

 water favored the i)henomenon, while drying the canal 

 through which the thermocouple was inserted into the tis- 

 sue prevented it. On the basis of these observations he 

 attributed the first freezing point to the congelation of the 

 extruded cell sap which surrounded the thermocouple. 



Zacharowa (1926), also using a thermocouple and fol- 

 lowing Maximov 's procedure, observed the same phenome- 

 non in roots of rye seedlings (Curve 3, Fig. 7). She 

 admits Maximov 's interpretation. 



Walter and Weismann (1936) confirmed the observa- 

 tions and interpretations of the previous investigators on 

 potato tuber. They used a mercury thermometer (Curve 

 4, Fig. 7). 



According to Mez (1905), one can observe, in the freezing 

 curves of plant tissues, two plateaus which correspond 

 respectively to the freezing and to the eutectic point of salt 

 solutions. 



Voigtliinder (1909), following Mez' views, presented a 

 vast amount of data which, wiien plotted, showed two 

 periods of retardation in the drop of temperature (rf. 

 Curve 5, Fig. 7). He took for granted that these periods 

 corresponded to the freezing and the eutectic points (F and 

 E in the figure). 



Luyet and Gehenio (1937) made a special study of the 

 factors involved in the doubling of the freezing point 



