Am"oS?iU.arm"}    Formation  of  Oxalic  Acid  in  Vegetation.  501 
salts  or  double  salts.  The  existence  of  soluble  oxalates  and  calcium 
salts  in  the  same  parts  of  a  plant  may  in  fact  be  explained  in  three 
ways.  The  oxalates  may  exist  in  the  form  of  double  salts  of  potas- 
sium, calcium,  and  magnesium,  dissociable  by  water,  or  the  formation 
of  oxalic  acid  may  take  place  in  special  vessels,  or  the  oxalic  acid  may 
oxist  in  the  form  of  ethereal  salts  which  are  ultimately  decomposed  in 
contact  with  calcium  compounds. 
When  the  plant  begins  to  fructify  (September  27th),  the  absolute 
amount  of  oxalic  acid  has  increased,  but  in  much  lower  proportion 
than  the  increase  of  the  whole  plant,  so  that  the  percentage  amount  is 
only  one-fourth  of  what  it  was  at  the  early  stage  of  growth.  The 
decrease  is  most  considerable  in  the  roots  and  limbs.  In  the  former, 
almost  all  the  oxalic  acid  is  in  the  insoluble  form,  whilst  in  the  limbs 
and  petioles  the  soluble  oxalates  preponderate.  At  the  same  time 
there  is  a  diminution  in  the  proportion  of  ash.  The  calcium  is  in 
excess  of  the  oxalic  acid  in  the  root,  but  in  the  petioles  and  stalks  the 
reverse  is  the  case.  The  limbs  are  rich  in  soluble  oxalates  and  also  in 
calcium  salts. 
The  leaves  of  R.  Acetosa  are  very  rich  in  nitrogenous  substances. 
They  are  also  the  principal  seat  of  the  formation  of  oxalic  acid, 
whereas  nitrates  undergo  destruction  in  the  leaves  {Ann.  Chem.  Phys. 
£6],  viii,  41).  It  would  seem  therefore  that  the  oxalic  acid  is  a  product 
of  the  incomplete  reduction  of  carbonic  acid.  If,  however,  the  ratio 
of  oxygen  expired  to  carbonic  anhydride  absorbed  remains  constant, 
the  production  of  oxalic  acid  in  this  way  would  require  the  simulta- 
neous production  of  some  highly  hydrogenized  compound  as  a  com- 
pensating reaction.  Such  hydrogenized  compounds  are  found  in  the 
albuminoids  which  are  so  abundant  in  the  leaves. 
Amarantus  caudatus. — This  plant  contains  a  considerable  propor- 
tion of  nitrates  (loc.  cit.)  and  the  oxalic  acid  is  mainly  in  an  insoluble 
form.  At  the  commencement  of  inflorescence  (June  18th)  the  per- 
centage of  oxalic  acid  was  5*86  or  about  half  that  found  in  R.  Acetosa. 
The  nitrates  are  found  chiefly  in  the  stalks  whilst  the  oxalates  are 
most  abundant  in  the  leaves  and  flowers.  As  inflorescence  progresses 
(July  26th),  the  amount  of  oxalic  acid  increases  in  proportion  to  the 
growth  of  the  plant  but  remains  almost  entirely  in  the  insoluble 
form.  When  inflorescence  was  fully  developed  (September  17th),  the 
total  weight  of  the  plant  had  increased  six-fold,  whilst  the  amount  of 
oxalic  acid  remained  the  same,  still  in  the  insoluble  form  and  existing 
