452  Structure  of  Our  Cherry  Barks.  {TePiSer%t 
Fig-  3- — Some  of  the  sclerenchymatous  elements  from  the  same  species, 
magnified  230  times;  the  longer  of  these  cells,  perhaps,  to  be  regarded  as  bast 
fibres,  or  as  transition  forms  between  stone  cells  and  bast  fibres. 
Fig.  4. — Starch  grains  from  bark  of  Prunus  serotina,  magnified  1,200  diam- 
eters. 
Fig.  5. — Cross-section  of  bark  of  Prunus  Mahaleb  magnified  about  75 
diameters,  a,  cork  exfoliating  from  exterior  surface  ;  b,  secondary  cork  forma- 
tion farther  interior  ;  c,  fissure  in  cortex  ;  d,  primary  bast  fibres  in  outer  portion 
of  bast  layer  ;  e,  compressed  sieve  tissue  ;  f,  single  bast  fibre.  (A  few  scattered 
bast  fibres  occur  in  the  secondary  bast  in  this  species.)  g,  medullary  ray;  h 
compressed  sieve  tissue  ;  i,  newly  formed  bast ;  k,  cambium  zone  ;  /,  large 
duct  in  newly  formed  wood  ;  m,  wood  of  previous  season. 
Fig.  6. — Tangential  section  through  bast  layer  of  Primus  Mahaleb,  showing 
medullary  rays  and  compressed  sieve  tissue.  Magnification  about  230  diameters. 
a,  compressed  sieve  tissue  ;  b,  crystal  cell  ;  c,  ordinary  parenchyma  cell  of 
medullary  ray  ;  d,  compressed  sieve  tissue  ;  e,  fissure  between  medullary  ray 
and  sieve  tissue. 
Fig.  7. — Cross-section  of  outer  part  of  bark  of  Prunus  Mahaleb,  showing 
mode  of  cork  formation,  a,  outer  layers  of  cork  exfoliating  at  the  surface  and 
showing  stratification  lines.  (The  cork  readily  splits  along  these  lines.)  b, 
cortex  or  middle  bark  ;  c,  cluster  of  primary  bast  fibres  ;  d,  secondary  cork 
forming  interior  to  the  clusters  of  primary  bast  fibres  ;  e,  compressed  sieve 
tissues.    Magnification  about  75  diameters. 
Fig.  8. — Small  portion  of  cross  section  of  inner  layer  of  stem  bark  of  Prunus 
Avium,  magnified  about  230  diameters,  showing  arrangement  of  bast  fibres. 
a,  portion  of  medullary  ray,  well  toward  the  outside  of  the  bast  layer  :  b,  com- 
pressed sieve  tissues  ;  c,  bast  fibre  ;  d,  parenchyma  cell ;  e,  bast  fibre,  in 
oblique  view. 
Fig.  g. — Some  of  the  sclerenchyma  fibres  as  they  appeared  i?i  situ  in  a  longi- 
tudinal tangential  section  of  the  bark  of  Prunus  Avium.  Magnification,  about 
230  diameters.  The  more  regular,  slender  and  elongated  fibres  usually  occur 
in  masses. 
Fi%.  10. — Starch  grains  of  P.  Avium  magnified  1,200  diameters. 
Fig.  11. — Cross-section  of  the  stem  bark  of  Prunus  Pennsylvanica  magnified 
about  75  diameters,  a,  cork  in  layers,  represented  as  separating  from  the 
middle  bark,  b ;  c,  irregular  or  tortuous  sclerenchyma  fibres  ;  d,  medullary 
ray ;  g,  fissure  between  medullary  ray  and  bast ;  h,  compressed  sieve  tissue  ; 
i}  young  bast  tissues  near  cambium  ;  k,  cambium  zone  ;  /,  a  duct  in  the  wood. 
Fig.  12. — Portion  of  longitudinal  tangential  section  of  inner  bark  of  P. 
Pennsylvanica  magnified  about  75  diameters,  a,  medullary  ray  ;  b,  soft  bast 
cell ;  c,  bast  fibre  ;  d,  crystal  cell. 
Fig.  13. — Starch  from  bark  of  Prunus  Pennsylvanica  magnified  1,200 
diameters. 
Fig.  14. — Cross  section  of  stem  bark  of  P.  Virginiafia,  magnified  about  75 
diameters,  a,  periderm  ;  b,  outer  cortex  (collenchyma) ;  c,  d,  tortuous  scleren- 
chyma fibres  ;  e,  medullary  ray  ;  f,  sclerenchyma  fibre  ;  g,  large  mass  of  sec- 
ondary bast  fibres  ;  h,  compressed  sieve  tissues  separating  masses  of  bast  fibres; 
i,  younger  bast ;  k,  cambium  zone  ;  /,  duct  in  newly  formed  wood  ;  m,  mature 
wood. 
