As"ptJeTbefS-}     Structure  of  Our  Cherry  Barks,  447 
even  extending  into  the  middle  bark,  but  clusters  and  isolated  fibres 
occur  abundantly  throughout  the  bast.  Many  of  the  fibres,  espe- 
cially those  occurring  in  bundles,  are  long  and  slender,  and  run  quite 
regularly  lengthwise  of  the  bark  ;  but  others,  especially  the  isolated 
ones,  are  very  irregular  in  form,  tortuous  in  their  course,  and  often 
branching. 
Fig.  12. — From  longitudinal  tangential  section  of  inner  bark  of  Primus 
Pennsylvanica. 
The  masses  of  bast  fibres  are  never  very  large,  and  are  not 
arranged  with  any  apparent  order. 
Crystals  of  calcium  oxalate  in  the  specimens  examined  were 
much  less  abundant  than  in  P.  serotma,  and  they  were  nearly  always 
in  stellate  masses. 
The  specimens  studied  were  gathered  in  June  and  July,  and  in 
these,  starch,  though  present  in  the  medullary  ray-cells,  was  not 
