WOODY STEMS 



245 



cambium (5) is typical in form, and it has formed one or two 

 layers of phelloderm cells (6) which have the same form as the 

 cambium cells but with thicker walls. Next to the phelloderm 

 occur the cortical parenchyma cells. The remaining structure 

 of the mature stem is identical with that of Fig. 2. 



POWDERED BUCHU STEM 



Powdered buchu stem (Plate 102) has many striking features 

 which make it easy of identification when mixed with buchu 

 leaves. A few unicellular, rough, thick, white-walled trichomes 

 (1) occur distributed throughout the field. They are straight 

 or shghtly curved and vary in length from 40 to 100 microns; 

 in thickness at the bast they measure from 10 to 22 microns. 

 The central cavity varies greatly, and in some trichomes seems 

 to have disappeared entirely. The epidermal cells (2) are very 

 characteristic, occurring singly or in groups of two or more. 

 The cells from the older stems often appear reddish brown by 

 transmitted light, while the epidermal cells from the younger 

 stems appear whitish opaque (porcelain-like) . They are usually 

 six-sided and angular in outline. The cortical parenchyma 

 cells (3) on transverse view have a rounded cell cavity and 

 intercellular spaces between the walls. The double walls vary 

 in thickness, the greatest thickness being about 9 microns. The 

 parenchyma cells (3) on longitudinal view show square ends 

 and often contain sphaero-crystalline masses of hesperidin. The 

 thin-walled sieve cells and the surrounding cells are scarcely 

 ever seen in the powder. The white- walled pointed stereomes 

 (4) are a characteristic feature of the powder ; they vary greatly 

 in length, in diameter and in the thickness of their walls. In 

 a number eighty powder the fibres are mostly broken. The 

 greatest length of the unbroken fibres is 1.25 microns. The 

 thickest wall measured 5 microns and the greatest observed 

 width was 25 microns. The spiral reticulate and scalariform 

 thickened conducting cells occur scattered throughout the 

 powder. The reticulate and scalariform cells usually occur with 

 wood fibres. It is an interesting fact that the spiral thickening 

 in conducting cells is usually separate from the side wall and 

 nearly always appears as indicated at 5. An occasional rosette 

 crystal of calcium oxalate (6) is seen in the field. The wood 



