TREES IN WINTER. 



83 



a pressure which forces the sap into every twig of 

 the tree. The most fa- 

 miliar illustration of the 

 flow of sap in the spring 

 is the Sugar-Maple. The 

 pressure of the sap forces 

 a stream of liquid to flow 

 from holes bored in the 

 bark of the tree. The old 

 idea that the sap descends 

 into the root of a tree in 

 the fall, and rises in the 

 spring, is erroneous. 



Then follows the most 

 striking phenomenon of 

 the whole year. The mild 

 days come. The supply of food in 

 the twigs is drawn up by the buds ; 

 they swell, they burst, and the leaves 

 begin to expand. A single week 

 has wrought a miracle whose wonder 

 never grows less. It has always 

 been the symbol of spiritual renewal 

 and the source of poetry, and it will 

 ever be so, however far we may trace 

 the physical causes of the change. 



FIG. 16. BRANCH 

 OF CHERRY. 



