78 



Table 25. Showing the Moisture Content of the Cortex in 

 November, January and May. 



It will be seen that there is no constant difference in moisture 

 content of the twig cortex from November to May. The difference 

 in the hardiness of the cortex can not be accounted for by the differ- 

 ence in the moisture content, but must be accounted for in some 

 other way. The suggestion is sometimes made that a greater sap 

 density of the twig and other tissue during winter might account 

 for this greater hardiness. It was not possible with our apparatus, 

 at least, to secure sap from the sap wood. The cortex, however, 

 shows this increase in hardiness to a slightly greater extent than 

 does the sap wood. The following table shows the cortex sap density 

 of apple and peach twigs at various seasons of the year, through a 

 period of three years: 



