74         ON  CELLULOSE  AND  THE  COMPOSITION  OF  WOOD. 
ceding,  was  washed  with  ammoniacal  water,  to  remove  as  far  as 
possible  the  oxide  of  copper.  In  a  third  experiment,  the  pith 
was  simply  cut  into  extremely  thin  laminae,  not  exceeding  from 
one  to  three  millimetres  in  thickness,  and  agitated  in  the  copper 
solution.  In  the  course  of  an  hour  it  commenced  to  dissolve, 
and  51  per  cent,  of  the  tissue  was  obtained  in  solution.  M. 
Payen  is  prepared  to  admit  that  very  great  differences  exist  be- 
tween different  kinds  of  cellular  tissue,  and  that  the  properties 
of  the  cellulose  will  constantly  vary  with  the  age,  the  thickness 
of  the  cell  walls,  the  amount  and  the  kind  of  incrusting  matter, 
and  the  associated  inorganic  constituents  ;  but  that  difference  in 
the  action  of  a  single  solvent,  such  as  cuprate  of  ammonia,  is 
totally  insufficient  to  establish  the  existence  of  a  distinct,  although 
isomeric,  species  of  cellulose. 
M.  Fremy,  in  his  memoir  on  the  composition  of  wood,  instead 
of  assuming,  as  physiologists  have  hitherto  done,  that  the  various 
tissues  of  the  plant  are  on  a  basis  of  cellulose,  which  is  variously 
associated  and  impregnated  with  foreign  substances,  considers 
that  each  tissue  presents  a  particular  chemical  composition,  and 
special  properties  depending  in  some  manner  on  the  peculiar 
physiological  part  which  it  supports  in  vegetation.  He  has 
already  shown  that  the  vegetable  tissues  contain  a  principle, 
Pectose  (which  has  not  been  disputed),  and  which  has  been  con- 
founded with  cellulose  in  microscopic  observations.  His  analy- 
ses and  examination  of  the  cuticle  also  indicate  that  it  possesses 
a  distinct  and  peculiar  composition.  In  this  paper  M.  Fremy 
only  recognizes  under  the  name  of  cellulose  that  substance  which 
is  immediately  dissolved  by  cuprate  of  ammonia,  and  which  con- 
stitutes cotton,  cortical  fibres,  or  the  perisperm  of  the  Phytele- 
phas.  The  substance  which  constitutes  the  pith  of  trees,  and 
which  is  insoluble  in  the  copper  solution,  he  names  Para-cellulose. 
Knowing  that  experiments  made  upon  a  mixture  of  different 
organic  tissues  might  lead  to  grave  errors,  M.  Fremy  sought  to 
isolate  the  different  organs  of  which  wood  is  constituted,  and 
submit  them  to  separate  examination.  Botanists  consider  wood 
as  formed  of  fibro-vascular  bundles,  separated  one  from  the 
other  with  cellular  tissue,  divided  by  rays  running  from  the 
pith  to  the  centre.  In  certain  parts  of  this  ligneous  mass  are 
found  masses  of  fibre  unrolled  and  annular  or  punctated  vessels. 
