320 
Pharmacognosy  of  Echinacea. 
Am.  Jour.  Pharm. 
July,  1911. 
and  the  cells  are  interspersed  with  groups  of  from  one  to  three  of 
the  characteristic  stone  cells  already  referred  to,  the  groups  being 
somewhat  circularly  disposed.    The  cambium  zone  is  distinct,  con- 
FlG.  3. 
Cross  and  longitudinarsections  showing  the  different  forms  of  stone  cells. 
sisting  of  several  rows  of  thin-walled  cells.  The  xylem  occurs  in 
rays  made  up  of  small  interrupted  groups  of  tracheae  which  are 
separated  by  wood  parenchyma.  The  tracheae  are  from  eight  to  ten 
times  as  long  as  they  are  wide,  the  walls  for  the  most  part  being 
