Am.  Jour.  Pharm. ) 
Jan.,  1883.  J 
Researches  on  the  Jalaps. 
31 
ligneous  masses  splits  up  parallel  to  the  surface  of  these  masses,  and 
thus  originate  true  secondary  generating  zones,  which  produce,  on  the 
side  of  the  wood  some  rows  of  muriform  parenchyma,  and,  on  the 
other  side,  secondary  liber,  with  numerous  glands  containing  resinous 
and  crystalline  matter. 
In  the  most  swollen  parts  are  seen  important  layers  of  muriform 
parenchyma,  divided  tangentially  in  every  direction,  and  furnishings 
at  the  same  time,  liber  products  on  the  one  side  and  parenchymatous 
elements  on  the  other.  All  the  parenchymatous  cells  are  gorged 
with  starch,  and  the  tubercule  constitutes  an  important  alimentary 
reserve  for  the  plant. 
In  studying  the  upper  portion  of  the  tubercule  I  have  followed  the 
reverse  order,  and  starting  from  the  upper  extremity  descended  towards 
the  centre. 
The  transverse  section  made  at  the  top  extremity  of  the  tubercule 
shows  that  the  organ,  at  this  point,  has  the  structure  of  a  stem.  The 
primary  ligneous  mass  forms,  in  fact,  an  annular  zone  around  the 
centre  of  the  organ,  but  at  a  certain  distance  from  the  centre.  It  is 
formed  of  radiating  layers  grouped  in  badly  defined  bundles.  Each 
layer  of  primary  wood  comprises  three  or  four  contiguous  spiral  vessels 
disposed  radially,  the  most  slender  being  inside.  The  differentiation 
of  the  primary  ligneous  elements,  therefore,  has  proceeded  from  the 
centre  of  the  development  (indicated  by  the  most  slender  spiral  vessel) 
in  a  direction  which  passes  by  the  centre  of  the  organ,  but  which  leaves 
the  centre  of  development  between  the  centre  of  the  organ  and  the 
ligneous  layer.  The  centre  of  the  organ  presents,  therefore,  a  central 
crown  of  bundles  with  centrifugal  differentiation.  From  this  it  may 
be  concluded  that  the  organ  at  this  level  is  a  stem. 
Moreover,  at  the  top  of  the  cicatrices,  to  which  I  have  referred 
before,  is  observed  the  issue  of  four  bundles,  in  two  opposite  appen- 
dages on  each  side.  At  the  axil  of  each  of  these  appendages  a  bud 
that  is  frequently  developed  is  placed  between  the  two  bundles  in 
relation  with  the  bundles  of  the  stem.  In  the  interval  comprised 
between  the  point  of  issue  of  the  appendages  and  the  swollen  middle 
portion  of  the  tubercule  occurs  the  extinction  of  the  primary  ligneous 
layers  of  the  stem.  The  organ  becomes  tuberized  in  this  region  by 
the  same  process  as  in  the  inferior  portion. 
The  extinction  of  the  primary  ligneous  layers  of  the  stem  shows  that 
there  is  here  a  lower  termination  of  the  principal  stem.  Therefore^ 
