The Inner Structure of the Planttlet. SI 
It is in this layer that growth in diameter (71) of the stem 
occurs. The bark of plants having the cambium layer sep- 
arates readily from the wood, at times when growth is rapid, 
because the walls of the newly-formed cambium cells are 
fe td 
J 
Fie. 20. Showing transverse section of corner of a bean stem (Vicia faba). 
C, cambium layer; e, epidermis; Cu, cuticle; St, stoma. The dark, oval-shaped 
spots, extending both sides of the cambium layer are the vascular bundles; W, 
wood cells of the vascular bundles. Moderately magnified. (After Potter). 
extremely thin and tender. The slimy surface of growing 
wood, whence the bark has just been removed, is due to the 
protoplasm from the ruptured cells. In plants having more 
than one cotyledon, the cambium line is usually readily dis- 
cerned in cross sections of the stem,— though it is rather 
more distinct, and the bark is more readily separable, in 
woody than in herbaceous* stems. In the latter, the part 
* Stems that do not have the hard, firm texture of wood, as of the potato, rhu- 
barb, etc., are said to be herbaceous. 
