Am.  Jour.  Pharm. 
June,  1S9-5. 
Strticture  of  Sassafras. 
317 
Later  on,  however,  secondary  bast  fibres  are  formed,  but  these 
are  never  so  abundant  as  to  give  an  evident  fibrous  fracture  to  the 
inner  layer  of  the  bark.  They  are  scattered  without  apparent  order 
through  the  bast  wedges,  and  are  not  usually  clustered,  though 
occasionally  two  or  three  may  be  seen  in  juxtaposition. 
They  are  excessively  thick-walled,  and,  for  bast  fibres,  short,  their 
length  being  not  more  than  from  ten  to  fifteen  times  their  thickness* 
They  are  also  hard  and  brittle. 
If  the  bark  be  gathered  in  late  autumn  or  in  very  early  spring, 
the  parenchyma  cells  of  the  bark,  and  even  the  thinnish-walled  wood 
cells  and  medullary  ray  cells  of  the  meditullium,  are  found  to  be 
heavily  charged  with  starch  grains.  These  are  of  rather  small  size, 
and,  when  single,  are  spherical  or  spheroidal  in  shape,  with  a  central 
hilum,  which  sometimes  shows  a  few  stratification  circles  about  it. 
The  circles,  however,  are  usually  indistinct  or  wanting.  The  hilum 
is  usually  entire,  and  appears,  even  under  a  very  high  power,  as  a 
mere  point,  but  it  is  sometimes  angularly  fissured.  Compound 
grains,  however,  are  more  common  than  simple  ones,  the  commonest 
being  double  and  triple  ones,  though  more  complex  forms  are  not 
uncommon. 
In  most  structural  characters  the  wood  of  the  root  and  that  of  the 
stem  resemble  each  other  closely.  The  ducts,  which  are  mostly  of 
the  pitted  variety,  with  the  pits  closely  arranged,  are,  in  both,  of 
large  diameter,  and  usually  grouped  in  twos  or  threes,  but  some- 
times single.  They  agree  also  in  the  fact  that  the  walls  of  the  wood 
cells  do  not  become  so  strongly  thickened  as  they  do  in  many 
other  woody  plants,  and  in  the  fact  that  the  medullary  ray  cells  are 
of  rather  large  diameter  as  compared  with  the  wood  cells,  are  usually 
elongated  in  a  radial  direction,  and  are  finely  pitted.  The}'  differ 
chiefly  in  the  conspicuous  large-celled  pith  of  the  stem,  which,  of 
course,  does  net  occur  in  the  root  at  all,  and  in  the  fact  that  in  the 
stem  the  medullary  rays  are  rather  more  numerous  and  inclined  to 
become  fewer-rowed,  three-rowed  rays  being  seldom  found. 
The  differences  between  the  bark  of  the  stem  and  that  of  the  root 
are  more  conspicuous.  Besides  the  inevitable  difference  due  to  the 
presence  of  chlorophyll  in  the  middle  bark  of  the  former  and  its 
absence  in  the  latter,  and  the  difference  in  cork  formation  already 
alluded  to,  namely,  the  fact  of  its  much  more  tardy  formation  in 
