78 NATURE OF THE ANNUAL RINGS 



difference in the structure of the. cells of the spring and summer 

 wood is doubtless due to the large volumes of water that are 

 transported to the rapidly growing shoots, flowers, and leaves 



cfc 



FIG. 57. Diagram of a three-year-old stem of basswood cut so as to 

 show the structure in cross-section, C, in radial section, R, and in tan- 

 gential section, T; c, cortex ; ck, cork ; me, medullary ray in cross-section ; 

 mr, ray in radial section ; mt, ray in tangential section ; I, lenticels ; cam, 

 cambium zone; p, pith. H. O. Ha.nson. 



each spring. Later in the season a lessened volume of water 

 produces firmer and denser tissues. The age of a tree can gener- 

 ally be ascertained by counting the annual rings. However, two 



