CH. V] ANNUAL KINGS. 69 



as well as breadth every year, but a branch split lengthwise 

 does not show transverse horizontal marks in the wood 



TRANSVERSE SECTION OF THE WOOD OF THE LIME-TREE, 



to show the annual rings. 

 P, pith. 



R, E, lines of large vessels in the spring wood of the annual rings. 

 After Van Tieghem. 



where the year's growth begins, the tissues of one year are 

 continuous with those of the next. Or to take a simpler 

 example : if a builder were to build for a week and rest 

 for a week and so on, it would not be possible afterwards to 

 point to the places where pauses had occurred. But if he 

 always began with a course of big bricks and ended with 

 a course of small ones, the resting places would be 

 revealed. 



Much discussion has been held as to the physiological 

 meaning of the annual rings : it is clear why the tree 

 grows in summer when it has leaves with which to 

 assimilate, and light and heat with which it can work its 



