450  Structure  of  Our  Cherry  Barks.  {*gj>t™i*?£££' 
Crystals  of  calcium  oxalate  abound,  and  they  are  mostly  in  stel- 
late masses. 
The  starch  grains  are  similar  in  shape  to  those  of  P.  Avium,  but 
they  average  of  larger  size,  and  compound  forms  appear  to  be  some- 
what less  numerous. 
Stem  Bark  of  Prunus  Virginiana. — This  tree,  commonly  called 
Choke  Cherry,  on  account  of  its  very  astringent  fruit,  is  undoubt- 
edly often  confounded  with  the  Black  Cherry.  This  is  not  only 
because  it  is  often,  in  general  appearance,  similar  to  that  of  a  small 
black  cherry  tree,  but  because  its  flowers  and  fruits  are  similar  in 
size,  color  and  arrangement,  being  borne  in  both  cases  in  racemes. 
Our  pharmaceutical  nomenclature  also  adds  to  the  danger  of  con- 
fusion, the  name  Prunus  Virginiana  being  still  absurdly  retained  as 
the  pharmacal  name  of  the  drug  obtained  from  P.  serotina. 
There  is  no  real  reason,  however,  why  any  one  tolerably  familiar 
with  the  botanical  characters  of  the  two  species  should  confound 
them,  for  there  are  marked  differences.  P.  Virginiana  is,  in  the 
first  place,  a  much  smaller  tree,  in  fact,  usually  more  a  shrub  than  a 
tree,  though  sometimes  its  stem  attains  a  diameter  of  two  or  three 
inches.  Its  branches  and  trunk  are  not  so  dark,  being  rather 
grayish  than  blackish,  and  the  lenticels  are  much  less  numerous. 
Its  leaves  are  thin,  oval-oblong  or  ovate,  abruptly  pointed,  and 
sharply  serrate,  with  slender,  projecting  teeth,  while  those  of  the 
black  cherry  are  thickish,  oblong-lanceolate  or  oblong  and  taper- 
pointed,  but  less  abruptly  so  than  in  the  other  species,  and  the 
margins  are  serrate  with  incurved,  short  and  callous  teeth.  The 
serrations  on  the  leaves  of  Choke  Cherry  are  also  often  double, 
which  is  not  the  fact  with  those  of  the  Black  Cherry.  The  petals 
of  the  Choke  Cherry  are  more  rounded  than  those  of  the  Black 
Cherry. 
The  microscope,  however,  reveals  the  most  decided  differences  in 
the  structure  of  the  barks.  The  medullary  rays  in  P.  Virginianay 
which  are  three  or  four  cells  wide,  are  less  flexuous  than  in  P.  sero- 
tina, or  in  any  other  species  examined.  Proper  stone  cells,  so 
abundant  in  the  bark  of  the  Black  Cherry,  are  almost  wholly  absent 
from  the  bark  of  the  Choke  Cherry,  but  the  tortuous  sclerenchyma 
fibres,  similar  to  those  in  P.  Avium  and  P.  Pennsylvanica,  not  only 
abound  in  the  inner  bark,  but  in  the  cortex.  Bast  fibres  of  the 
ordinary  form  also  occur  in  large  and  irregular  masses  in  all  the 
