Am.  Jour.  Pharra.  \ 
April,  1897.  / 
Parthenium  Hysterophorous. 
171 
single  layers,  through  which  pass  branching  fibro-vascular  bundles, 
the  prominent  constituent  of  which  are  spiral  ducts.  The  scales 
terminate  in  a  mass  of  hairs  composed  of  two  to  four  cells,  of  which 
the  terminal  one  is  the  largest.  The  cells  of  the  corolla  of  the 
disc  florets  are  more  symmetrical  than  those  of  the  chaff,  the 
vascular  system  is  identified  by  the  spiral  ducts.    The  walls  of  the 
Fig.  2.    Ray  floret,  magnified  about  forty- eight  diameters. 
anther  cells  possess  reticulate  markings  which  are  quite  character- 
istic. The  pollen  grains,  as  mentioned  above,  are  prickled  {Fig.  4). 
A  cross-section  of  a  leaf  lobe  shows  the  prominence  of  even  the 
secondary  veins.  These  project  chiefly  on  the  under  side.  The 
closed  fibro-vascular  bundle  is  bi-  collateral.  The  lower  half  of  the 
leaf  is  of  spongy  parenchyma,  while  the  upper  consists  of  a  palisade 
layer  {Fig.  5).    The  epidermis  of  the  under  side  is  interrupted  by 
