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FORMATION  OF  GLUCOSE  BY  LEAVES. 
rhubarb  to  the  Yang-ti  plant,  says  that  the  stalk  is  crisp  and  sour 
and  may  be  chewed  raw.    Rheum  palmatum  is  not  cultivated  in 
England  for  culinary  use;  but  Mr.  Robinson,  of  the  Botanic 
Gardens,  Regent's  Park,  informs  me  that  he  has  seen  it  so  used 
in  Ireland. — Lond.  Pharm.  Jour.,  Jan.  1st.,  1866. 
ON  THE  FORMATION  OF  GLUCOSE  BY  LEA  YES. 
By  M.  Boussingault. 
The  supposition  that  the  production  of  glucose  and  its  con- 
geners is  principally  effected  by  the  aerial  organs  of  plants  is 
contradicted  by  the  abundance  of  saccharine  matter  in  the 
stalks,  the  roots,  and  especially  by  the  formation  of  the  same 
matter  during  germination,  when  the  leaves  are  not  yet  formed. 
But  the  germination  only  transforms  starch  into  glucose,  sugar 
and  cellulose  ;  it  brings  no  combustible  element ;  on  the  con- 
trary, the  embryo,  for  its  nourishment,  consumes  those  pre- 
existent  in  the  seed. 
By  looking  at  the  vegetable  world  in  its  entirety,  one  is  con- 
vinced that  the  leaf  is  the  first  resting-place  of  the  glucosides, 
which,  more  or  less  modified,  are  found  scattered  in  various 
parts  of  the  organism ;  that  it  is  the  leaf  which  elaborates  them, 
at  the  expense  of  the  carbonic  acid  and  water.  In  maize, 
wheat,  &c,  the  accumulation  of  saccharine  principles  takes 
place  in  the  stalk,  up  to  the  time  of  flowering,  when  all  that  has 
been  formed  assists  in  the  formation  of  the  seed.  In  beet  root, 
this  receptacle  is  the  principal  fleshy  root.  But  where  there  is 
neither  stalk  nor  root,  where  is  the  saccharine  matter  formed  by 
the  leaf  deposited  ?  In  the  leaf  itself,  which  is  then  consider- 
ably extended.  The  most  striking  example  is  presented  by  the 
American  agave,  the  maquey,  the  vine  of  the  Mexicans,  the 
culture  of  which  extends  from  the  time  of  Montezuma  and 
further.  The  leaves  of  the  agave  all  grow  from  the  neck  of  the 
root ;  they  attain  two  metres  in  length,  twenty  centimetres  in 
breadth,  and  one  decimetre  at  the  point  of  attachment.  During 
from  fifteen  to  twenty  years,  these  leaves  elaborate  and  accumu- 
late glucose,  until  the  stalk  which  is  to  bear  the  flowers  and 
fruits  begins  to  form.    Then  the  large,  coriaceous,  prickle-edged 
