Chapter VIII 



121 



Active Relations 



pressible from living leaves was much less during the winter months than 

 during the summer. This suggested, as did Newton's data, that the pres- 

 sure method may be useful in estimating cold hardiness in plants. The 

 explanation that the proportion of coUoidally (gel) bound water was greater 

 in winter was substantiated by the increased difficulty experienced in freez- 

 ing the leaves. Meyer's results are shown in Figure 37. 



loo 



90 



80 



70 ■ 



60 



<0 



SO 



^0 



30 



20- 



10 



^f\ug, ^ept Oct. Nov. Dec. Jan. Feb. Han flpKMcfy June July 



Fig. 37. — Seasonal variations in the dry matter content, inexpressible water, and 

 water expressed as sap after different treatment of leaves of Pinus rigida. A, volume 

 of sap expressed from unfrozen leaves; B, additional sap expressed from leaf samples 

 frozen in an ice-salt bath; C, additional sap expressed from samples frozen in solid 

 carbon dioxide; D, inexpressible water; E, dry matter content. Pressure, 5000 pounds 

 per square inch. Data of Meyer (1928). 



Later (1932) Meyer attempted to demonstrate a correlation between 

 cold resistance in pine and the amount of bound water detectable by the 

 calorimetric method. By this method there was a slightly greater amount 



