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STRUCTURAL BOTANY 



The secondary wood is of simple structure compared 

 with that of most Dicotyledons. Ib consists entirely 

 of tracheides and medullary rays ; there are no vessels, 

 and there is no woody parenchyma, but the wood is 

 traversed by resin canals, which have their secretory 

 epithelium. The tracheides are long, pointed elements, 



FIG. 98. Radial section of the wood and bast of the Scotch Fir 

 (Pinus sylvestris). xy, xylem ; c, cambium ; ph, phloem j 

 a, r.s, a to t, s, t, medullary ray ; t, t, tracheides of ray ; 

 s, starch-containing cells ; a. a, albuminous cells ; r.s, 

 starch-containing cells. Magnified. (After Strasburger.) 



reaching a length of from two to four millimetres ; 

 they are as a rule pitted on their radial walls only. 



The pits are of the bordered kind, and afford the 

 best examples of this structure. On each radial wall 

 of the tracheide there is a single row of large bordered 



