io6 



PLANT ORGANS OR PARTS OF PLANTS. 



by a thin brownish periderm with a yellowish central woody 

 cylinder. The relative proportion of cortex to central 

 cylinder is an index of the character of the root. Those 



Fig. 20. — Ipecac. 

 Longitudinal section of Ipecac root: c, Cambium; AT, crystals; rp, 

 cortical parenchyma; hp, woody parenchyma; hf, wood fibres; m, 

 medullary rays; tr, tracheids with border pores (Moeller). 



roots with thicker cortex are considered of better 

 quality than those with thinner cortex, since the active 

 principles are present almost exclusively in the cortex 



