CHAPTER III 

 WOODY STEMS 



BUCHU STEM 



The cross-section of a buchu stem (Plate C), 1.6 millimeters 

 in diameter, shows a few of the epidermal cells modified into 

 thick- walled, roughish, unicellular trichomes (i). The remain- 

 ing epidermal cells have a thick, wavy outer wall (2). Beneath 

 the epidermis are several rows of cortical parenchyma cells (3) 

 which extend to the bast bundles and in which are found the 

 secretory cavities with the thin- walled secretory cells (4). The 

 bast fibres (5) occur in continuous bands, varying greatly in size; 

 the walls are whitish and of variable thickness. Inside the 

 bast fibres, the small irregular sieve cells (6) occur in groups, 

 surrounded by the phloem parenchyma (8). The radially 

 elongated cells of the medullary rays (7) extend outward from 

 the xylem, increasing in number in the outer portions of the 

 wood, and extending nearly to the bast fibres. No distinct 

 cambium layer is visible. The conducting cells (9) occur 

 throughout the xylem surrounded by the wood fibres and wood 

 parenchyma (10). The latter is not very abundant in buchu. 

 The medullary rays border on the conducting cells and extend 

 outward to the phloem. The pith parenchyma cells are nearly 

 circular in outline and often show a perforated end wall when 

 a cell happens to be cut just above or below that point. 



MATURE BUCHU STEM 



In Plate loi-A is shown the cork formation or secondary 

 growth as seen in the older, larger buchu stems. The wavy 

 epidermis (i), which is the primary epidermis and which has 

 disappeared on many portions of the stem, has thin side walls 

 and dark cell contents (2). Next to the epidermal cells occur 

 several rows of peculiarly arched cork cells with thick, white 

 outer walls (3) and reddish-brown cell contents (4). The cork 



242 



