120 



THE STEM. 



I. In the Wood : 



1. The Pith, belonging to the cellular system (Fig. 159, 160,7?). 



2. The Medullary Sheath, ins, ) which belong to the woody or 



3. The Layer of Wood, W, w, \ longitudinal system. 



4. The Medullary Rays, mr, a part of the cellular system. 



II. In the Bark : 



5. The Liber, I ; its bast tissue, b, belongs to the woody system. 



6. The Outer Bark, belonging wholly to the cellular system, 



and composed of two parts ; namely, 1st, the Green or Cel- 

 lular Envelope, ge, and 2d, the Corky Envelope, ce. 



7. The Epidermis, e, or skin, which invests the whole. 



159 



FIG. 159. Portion of a transverse section, and 160, a corresponding vertical section, magni- 

 fied, reaching from the pith, p, to the epidermis, e, of a stem of Negundo, a year old: B, the 

 bark; W, the wood; and C, the cambium-layer, as found in February. The references are in 

 the text above ; except mr, portion of a medullary ray, seen on the vertical section, where it 

 runs into the pith : dd, dotted ducts : cl, the inner part of the cambium-layer, which begins 

 the new layer of wood In this tree, we find a thick layer of parenchyma (/) inside of the bast 

 tissue, and therefore belonging to the liber. No bast tissue is formed in it the second year. 



