boussingalt's  researches  on  the  action  of  foliage.  463 
in  cellulose,  starch,  sugar,  &c,  i.  e.,  in  the  important  principles 
elaborated  by  the  leaves,  the  composition  of  which  is  represented 
by  carbon  and  water.  He  goes  on  to  prove  that  a  leaf  which 
has  been  decomposing  carbonic  acid  and  water  all  day  long  is 
capable  of  doing  the  same  work  the  next  day,  if  not  allowed  to 
dry,  but  the  losing  of  a  certain  amount  of  water  annihilates  this 
faculty,  and  irremediably  destroys  the  life  of  the  cells  of  a  leaf, 
vegetable  life  in  this  state  being  far  less  tenacious  than  that  of 
some  of  the  lower  animals  (Tardigrades,  Notifies,  &c),  which 
bear  wonderful  desiccation. 
The  third  instalment  of  the  investigation  is  given  in  Nos.  16 
and  17  of  the  same  volume  (Oct.  16  and  23,  1865).  It  appears 
that  detached  leaves,  kept  in  shade  for  many  days,  with  the  cut 
end  of  the  petiole  in  water  to  prevent  desiccation,  preserve  the 
power  of  decomposing  carbonic  acid  whenever  brought  into  sun- 
shine. But  for  this  they  must  be  kept  in  an  atmosphere  con- 
taining a  supply  of  oxygen  ;  without  this  they  soon  die,  as  Bous- 
singault  thinks,  from  asphyxia.  The  oxygen  in  darkness  is 
slowly  transformed  into  carbonic  acid,  through  an  operation 
which  is  presumed  to  go  on  continually,  whether  in  light  or  dark- 
ness, and  to  answer  to  respiration.  Of  course  a  healthy  and 
active  leaf  decomposes  far  more  carbonic  acid  in  the  light  than 
it  forms  in  darkness.  In  eighteen  experiments,  with  Oleander- 
leaves  exposed  to  the  sun  from  8  A.  M.  to  5  P.  M.;  in  an  at- 
mosphere rich  in  carbonic  acid,  a  square  meter  of  foliage  decom- 
posed on  the  average  over  a  litre  of  carbonic  acid  per  hour, 
while  in  darkness  only  of  a  litre  of  carbonic  acid  was  pro- 
duced per  hour.  In  air  which  contains  oxygen  and  carbonic 
acid,  leaves  will  go  on  indefinitely  producing  oxygen  in  the 
presence  of  carbonic  acid,  and  carbonic  acid  in  the  presence  of 
oxygen.  But  the  latter,  though  relatively  small  in  amount, 
seems  to  be  necessary  to  the  preservation  of  their  vitality.  In 
hydrogen,  carburetted  hydrogen,  or  nitrogen,  as  well  as  in  pure 
carbonic  acid,  they  soon  lose  their  decomposing  power,  and 
die  from  the  impossibility  of  respiration,  i.  e.,  are  asphyxiated. 
Leaves  confined  in  a  limited  portion  of  atmospheric  or  other 
air  over  mercury  lose  the  power  of  decomposing  carbonic  acid ; 
