hardiness of the older leaves. In fact the following table, giving 

 results where twigs with young leaves were placed in cane sugar and 

 glycerine solutions, indicates that increasing the sap density of the 

 young leaves to that of the old leaves will increase their hardiness 

 to nearly that of the old leaves. 



Table 28. Showing Relative Hardiness of Young and Old 



Apple Leaves and of Young Leaves that had 



Absorbed Glycerine and Cane Sugar. 



In case of lettuce, however, the depression for old leaves was 

 0.575, and for young leaves 0.520, and the young leaves are the most 

 resistant to the low temperatures. It is possible that the waxy 

 or oily covering on the surface of the young lettuce leaves increased 

 their resistance to low temperatures. In our experience leaves and 

 fruits dipped in glycerine or paraffine have been uniformly more 

 resistant than have tissues not so treated. 



