204 
North  American  Coniferce. 
Am.  Jour.  Pharm. 
April,  18C6. 
species  of  pines.  The  resin  ducts,  usually  one  opposite  each  angle  of 
the  leaf,  and  often  one  opposite  the  middle  of  the  convex  side,  were 
buried  in  the  mesophyll  nearly  midway  between  the  endodermis 
and  hypoderma,  and  each  was  usually  bounded  by  a  strengthening 
layer  of  thick-walled  cells.  Endodermis  with  cell  walls  scarcely 
thickened,  except  the  radial  walls,  which  were  somewhat  so ;  trans- 
fusion tissue  of  the  usual  pitted  variety,  enclosing  two  diverging 
bundles,  each  crossed  by  two  or  three  medullary  rays.  Buried  in 
the  transfusion  tissue,  between  the  outer  ends  of  the  phloem  of  the 
two  bundles,  were  a  few  thick-walled  fibres,  and  a  few  were  also 
Fig.  ig,  transverse  section  of  leaf  of  Piuus  Taeda,  magnified  100  diameters. 
►S"/,  stoma ;  by  a  cell  of  the  outer  of  the  two  layers  of  the  hypoderma  ;  sec.  r, 
secretion  reservoir. 
found  between  the  inner  ends  of  the  xylem  masses  of  the  two 
bundles.  The  mesophyll  cells  were  observed  to  contain  tannin  in 
abundance,  in  this  respect  resembling  all  the  other  species  ex- 
amined. 
A  transverse  section  of  a  twig  of  two  years'  growth  showed  the 
following  structure:  An  epidermis  composed  of  small  but  very 
thick-walled  cells,  supported  interiorly  by  several  layers  of  cells 
with  excessively  thickened  walls.  These  were  succeeded  interiorly 
by  several  layers  of  rather  large,  thin-walled  cells,  next  to  which 
occurred  another  zone  of  very  thick-walled  cells,  apparently  an 
