STRUCTURE OF THE STEM 



101 



(6) The narrow lines running in very young stems 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.i 



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



(d) 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- 





) [ 



^ j.^ 



Fig. 72. — Cross-Section of Beeoli-Wood. 

 b, bark ; a, flattened cells formed near 

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

 lar wood-cells ; m, medullary ray. 



Fig. 73. — Longitudinal Section of 

 Mahogany at Bight Angles to 

 Medullary Bays, 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 K. B. Hough, Lowville, N. Y. 



