57.  These  strings  of  denser  tissue  correspond  to  the  areas
which  are  colored  by  the  dye.  They  are  in  the  form  of  minute
bundles,  and  are  called  vascular  bundles.
50


PHYSIOLOGY.
;  97-  We  thus  !iee  that  instead  of  the  liquids  passing  through
the  entire  stem  they  are  confined  to  definite  courses.  Now  that
we  have  discovered  the  path  of  the  upward  nwveraent  of  water
in  the  stem,  we  are  curious  to  see  what  the  structure  of  these
definite  portions  of  ihe  stem  is.
98,  Btrnotara  of  the  flbra-vuctilar  bondle*. — We  should  now  make  quite
thin  cross  sections,  either  free  hand  and  mount  in  water  for  microscopic
or  tliey  may  be  mide  with  a  microtome  and  mounted  in  Canada
Tl  tliis  condition  will  answer  for  future  study.  To  illustrate  the
-c  of  the  bundle  in  one  type  we  may  take  the  stem  of  the  castor-tHl
bean.  On  vxamining  these  cross  sections  we  see  that  there  are  gifMpS  of
cells  which  are  denser  than  the  ground  tissue.  These  groups  correspond  to
the  colored  areas  in  the  former  experiments,  and  are  the  vascular  bundles


isa.  These  groups  arc
end  <fir<:cled  lownrd  llie  cciii
u  ■  whole  we  see  thai  lliere


'  of  uwtll  celli


•This  ring  and  the  bundles  separate  Ihe  sle
one  composeitof  lar^  cells  with  thin  walls,  ki
collectively  the  cerUx.  Tlie  iimer  portion,  toi
the  pith.  Is  made  up  of  tlie  same  klnil  of  cells
/■ilk.  When  the  cells  of  the  cortex,  as  well  as  of  llie  pith,  remain  thin  walled
the  tissue  is  callnl  paruncliyma.  Parenchyma  belongs  to  the  group  ol
tissues  calli'il  fund  a  mental.
