160    UREA  AS  A  DIRECT  SOURCE  OF  NITROGEN  TO  PLANTS. 
It  is  not  a  little  suggestive,  that  the  Chinese,  so  remarkable 
for  their  admirable  economy  of  the  natural  manures,  apply  the 
urine  to  the  land  in  an  unfermented  state.  And  the  most  casual 
thinker  will  readily  understand  that  it  must  be  wiser  to  apply 
it  in  this  state  than  after  a  large  proportion  of  its  nitrogen  has, 
as  a  constituent  of  ammonia,  escaped  into  the  atmosphere.  Be- 
sides, they  avoid  the  unnecessary  expense  of  constructing  costly 
liquid-manure  tanks. 
Independently  of  the  experiments  which  I  have  made  on 
urea,  our  knowledge  of  the  composition  and  properties  of  the 
constituents  of  urine  should  have  led  a  priori  to  the  conclusion 
that  these  are  for  the  most  part  in  that  digestible  form  in  which 
they  can  be  taken  up  into  the  organisms  of  plants. 
My  own  labors  and  those  of  others  have  led  me  to  conclude 
that  substances  capable  of  being  used  as  food  for  plants,  must 
possess  the  following  composition  and  properties  : — 
1.  — They  must  be  soluble  in  the  solvents  usually  present  in 
the  soil. 
2.  — They  must  contain  more  or  less  of  the  elementary  con- 
stituents of  vegetable  substances. 
3.  — They  must  be  in  a  perfectly  oxidized  {teleoxidic)  condi- 
tion. 
In  this  contribution  to  the  theory  of  manures,  I  have  advanced 
nothing  antagonistic  to  the  views  so  ably  advocated  by  Liebig 
on  the  subject  of  vegetable  nutrition  ;  on  the  contrary,  I  am  al- 
together disposed  to  believe  with  him  that  organic  substances 
cannot  minister  to  the  wants  of  vegetable  life.  I  do  not  regard 
urea  as  an  organic  substance,  any  more  than  I  do  carbonic  acid, 
cyanogen,  or  ammonia.  These  bodies,  as  well  as  urea,  may  be 
artificially  prepared  from  inorganic  materials  ;  they  are,  there- 
fore, not  organic  bodies,  but  rather  the  results  of  organic  action 
— the  ultimate  products  of  the  decomposition  of  organic  substan- 
ces. Carbonic  acid,  nitric  acid,  ammonia  and  the  cyanides 
have  been  proved  to  be  capable  of  supplying  nutrient  materials 
to  plants.  There  is  no  theoretical  reason  why  urea  should  not 
be  added  to  the  list.  It  is  soluble,  contains  the  four  principal 
elementary  constituents  of  vegetable  structures,  and  is  a  per- 
fectly teleoxidic  body.  It  therefore  possesses  the  composition 
and  properties  which  distinguish  the  "food  of  plants." — Lon- 
don Chemist,  Nov.  1858. 
