30  Researches  on  the  Jalaps.  {"^'j^n  ""isss^'""' 
here  only  to  the  formation  of  the  elements  of  the  liber.  Among  the 
young  cells  with  tangential  divisions  belonging  to  the  cambial  zone^ 
the  most  external  present  very  early  longitudinal  septa^  which  sub- 
divide them  into  a  number  of  narrow  elongated  cells^  such  as  are  seen 
in  the  Asclepiadacese,  Apocynacese,  Solanacese  and  Acanthacese.  The 
transverse  septum  which  separates  two  superposed  cells  is  reabsorbed^ 
following  the  meshes  of  the  tissue^  and  in  this  way  are  originated  the 
perforated  plates  of  cells  characteristic  of  the  liber.  The  elements  of 
the  cambial  zone  which  do  not  present  these  septa  make  up  the  liber 
parenchyma,  in  the  midst  of  which  occur  numerous  resiniferous  cells 
and  glands  containing  crystals. 
The  resin-cells  would  apj^ear  to  be  parenchymatous  elements,  hyper- 
trophied  and  gorged  with  resin.  Generally  they  are  superposed  end 
to  end,  so  as  to  form  rather  long  vertical  rows ;  but  in  no  case  have  I 
observed  the  reabsorption  of  the  wall  common  to  two  successive  cells. 
There  is  therefore  no  formation  of  a  canal,  and  I  look  upon  these  resin 
cells  as  unicellular  glands  distributed  in  the  mass  of  the  liber. 
The  crystal-bearing  glands  consist  of  parenchymatous  cells,  sub- 
divided into  as  many  compartments  as  they  contain  groups  of  crystals. 
These  groups  are  sphseraphides  of  oxalate  of  lime.  A  radial  section, 
treated  with  a  mineral  acid  which  dissolves  the  oxalate  of  lime^ 
shows  readily  the  subdivision  of  these  glands. 
I  will  now^  briefly  sketch  the  structure  of  the  part  of  the  tubercule 
comprised  between  the  lower  extremity  and  the  point  which  corres- 
ponds to  the  maximum  volume  of  the  organ,  setting  forth  the  mechan- 
ism of  the  formation  of  the  tuber. 
In  sections  which  follow  those  which  presented  the  structure  of  a 
well-characterized  root,  there  is  observed,  in  proportion  as  they  rise 
towards  the  central  part  of  the  tuber,  the  interposition,  among  the 
hardened  and  characteristic  elements  of  the  root,  of  a  parenchymatous 
tissue,  supplied  at  first  solely  by  the  cambial  zone.  The  interposition 
of  this  tissue,  which  I  will  call  the  muriform  parenchyma,^^  results 
in  separating  the  woody  layers  from  each  other,  and  quickly  interfer- 
ing with  the  primitive  symmetry  of  the  organ.  The  spiral  layers, 
carried  away  and  twisted  in  every  direction  by  the  secondary  ligneous 
lobes,  quickly  disappear,  so  that  at  a  very  short  distance  from  the 
lower  extremity  of  the  tubercule  it  is  already  impossible  to  recognize 
them. 
Higher  up  the  muriform  parenchyma  which  surrounds  the  indurated 
