WOODY STEMS 247 



parenchyma (7), which makes up a very small percentage of 

 the xylem, is not readily found in the powder. The pith paren- 

 ch}'Tma cells (8) have thick, porous side walls and perforated side 

 walls. The wood fibres (9) usually occur in masses surrounding 

 the conducting cells; when occurring singly, the oblique pores 

 readily distinguish them from the bast fibres. 



The diagnostic elements of powdered buchu stems are: 

 First, trichomes; secondly, reddish-brown and white-angled 

 epidermal cells; thirdly, the long, white bast fibres. 



