Am.  Jour.  Pharrn. 
July,  1895. 
}    Structure  of  Our  Hemlock  Barks. 
361 
those  of  adjacent  tissues ;  but  those  of  Tsuga  Mertensiana  are,  on 
the  average,  larger,  and  the  rays  in  this  species,  as  seen  in  a  longi- 
tudinal-tangential section  are  composed,  on  the  average,  of  a  larger 
number  of  cells.  These  differences  in  the  medullary  rays  are  per- 
haps the  most  constant  ones  between  the  two  barks. 
Both  barks  contain  abundance  of  crystals  of  oxalate  of  calcium. 
These  are  mostly  in  the  form  of  long  prisms,  and  are  contained  in 
QA- 
FiG.  5- 
rows  of  elongated  cells  of  narrow  diameter,  which  traverse  the  bark 
in  the  direction  of  its  length.  The  crystals  are  frequently  associated 
in  the  containing  cells  with  resinous  and  coloring  matters.  In  form 
and  arrangement  they  do  not  differ  in  the  two  barks,  but  appear  to 
be  rather  more  abundant  in  the  Pacific  Coast  species. 
Oleo-  resin  cells  appear  to  be  about  equally  abundant  in  the  two 
species.    Those  that  do  not  also  contain  crystals  are  isolated  or  in 
