^"■j'i'iy'^im*'^"''}        Pharmacognosy  of  Echinacea.  321 
marked  with  simple  slit-like  pores,  although  annular  and  reticulate 
markings  also  occur.  In  between  the  xylem  rays  occur  broad 
wedges  consisting  of  from  ten  to  twenty  radial  rows  of  parenchyma 
cells  that  are  not  of  the  type  of  medullary  rays.  Scattered  among 
these  cells  are  intercellular  oil  and  resin  reservoirs  and  more  or 
less  elongated  stone  cells  similar  to  those  already  referred  to.  In 
Fig.  4. 
Cross  section  of  root  showing  a  large  oleoresin  canal  (o) ,  tracheae  or  vessels  (/) ,  and  parenchyma  {p) . 
the  xylem  rays  true  wood  fibres  are  also  associated  with  the  tracheoe 
in  certain  specimens  collected  in  Tennessee  and  Missouri.  The 
wood  fibres  are  readily  distinguished  from  the  stone  cells  by  reason 
of  their  position,  more  uniform  outline  and  attenuated  ends.  In 
very  young  roots,  in  which  the  primary  structure  is  still  unchanged, 
the  fibrovascular  strand  is  of  the  triarch  type. 
