CHAPTER III 
WOODY STEMS 
BUCHU STEM 
The cross-section of a buchu stem (Plate C) 1.6 millimeters 
in diameter, showing a few of the epidermal cells modified into 
thick-walled, roughish, unicellular trichomes (1). 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 1o1-A is shown the cork formation or secondary 
growth as seen in the older, larger buchu stems. The wavy 
epidermis (1), 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 
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