STRUCTURE OK THE S 



101 



(b) The narrow lines running in very young sterns pretty straight 

 from pith to bark, in older wood extending only a little of the way 

 from center to bark, the medullary rays, shown in Fig. 72. J 



(c) The wedge-shaped masses of wood between these. 



(r/) The pores which are so grouped as to mark the divisions 

 between successive rings. These pores indicate the cross-sections of 



vessels or ducts. Note the dis- 

 tribution of the vessels in the 

 rings to which they belong, com- 



Fi<;. 7-2. Cross-Section of Beech- Wood. 



b, bark ; a, flattened cells formed near 

 end of each year's growth ; w, regu- 

 lar wood-cells ; HI, medullary ray. 



FIG. 73. Longitudinal Section of 

 Mahogany at Eight Angles to 

 Medullary Rays, showing Cut- 

 off Ends. (Much magnified.) 



pare this with Figs. 58, 72, and decide at what season of the year 

 the largest ducts are mainly produced. Make a careful drawing 

 of the end-section of one billet of wood, natural size. 



Cut off a grapevine several years old and notice the great size of 



1 These and many other important things are admirably shown in the thin 

 wood-sections furnished for $4 per set of 24 by R. B. Hough, Lowville, N. Y. 



