I3 6 SCOTCH PINE. 



iv. In some sections one or more distinct whitish 

 bundles passing out from the center of the 

 stem. Notice that a continuation of the cen- 

 tral pith occupies the center of each. Observe 

 the relation of these bundles to the scars on 

 the bark indicating the position of former 

 dwarf shoots. If the stem be four or more 

 years old, note that the bundles stop quite 

 abruptly at the close of the second year's 

 growth. 



c. All the part outside the wood, the bark. Distin- 

 guish its three layers : 



i. The inner fibrous layer, whitish. Notice its 

 appearance and thickness relative to the 

 whole bark. 



ii. The middle, green layer. Notice the large 

 resin ducts. (In fresh specimens note the 

 color, consistence and odor of the liquid they 

 exude.) Compare the thickness of this layer 

 with that of the first. 



iii. The outer brownish layer, except in quite old 

 stems made by the adherence of the bases of 

 the scale leaves. Note its relative thickness, 

 iv. Strip off a portion of the bark. The three 

 layers may be easily separated with the 

 fingers. Study the characteristics of each. 



d. Bisect the stem longitudinally. On the cut sur- 

 face and in thin sections make out the pith, wood 

 and bark ; the growth rings, medullary rays, and 

 bundles extending toward bases of former leaf- 

 branches, in the wood ; the three layers of the bark. 



e. Make drawings of the transverse and longitudinal 

 sections to show completely the structure of the 

 stem. 



