366 



THE SPERMATOPHYTES 



351. The tissues of the pine stem. The pine is an excellent 

 subject for the study of stem structure and growth in a timber 

 tree. There are five principal regions in the stem: (1) the pith, 



FIG. 297. Structure of the stein of the Scotch pine (Pinus sylvestris) 



A, diagram of the arrangement of the fibre-vascular bundles at a growing point : 

 the shaded parts are wood. .B t diagram of the position of the principal tissues 

 shown in a cross section of a four-year-old stem. C, cross section of a region 

 of cambium Cam, with adjacent wood and bast. D, cross section of wood at 

 an annual ring: d, resin duct. E, radial section of wood. F, longitudinal sec- 

 tion of wood. G, section of bordered pit. Medullary rays m appear in most 

 of tbe figures 



(2) the wood, (3) the cambium, (4) the bast, and (5) the outer 

 bark (see Fig. 297, #). 



The pith occupies the very center of the stem, and is the 

 remains of the undifferentiated primitive tissue present at its 



