50  Oxidisable  Constituents  of  Plants.         {Am  j™*^*™' 
air  inmediately  of  a  dirty  wine-red  color,  then  violet,  brown  and  finally 
almost  black.  These  facts  indicate  the  presence  in  plants  of  easily  oxidis- 
able bodies,  and  inasmuch  as  the  products  of  their  oxidation  do  not  occur 
within  the  uninjured  cells,  it  follows  that  there  is  either  no  free  oxygen  in 
the  latter,  or  that  with  these  oxidisable  substances  other  reducing  substances 
are  concomitant,  hindering  their  oxidation,  or  again,  that  in  the  protoplasm 
oxidation  affords  other  uncolored  products.  Upon  which  of  these  three 
factors  the  colorless  state  of  the  protoplasm  and  cell-juice  of  living  plants 
depends  is  not  yet  decided. 
In  the  study  of  oxidation  processes  in  the  living  plant-cell,  an  important 
question  presents  itself,  as  to  whether  substances  occur  in  the  cell  which  at 
ordinary  temperatures  unite  with  atmospheric  oxygen  without  the  essential 
co-operation  in  this  process  of  the  living  protoplasm.  Difficult  as  the  pro- 
blem is,  the  isolation  and  determination  of  constitution  of  these  easily 
oxidisable  substances  forms  an  indispensable  preliminary  step.  It  may  be 
conjectured  that  they  belong  to  the  aromatic  series.  In  this  connection  the 
numerous  hydroxybenzene  derivatives  claim  attention,  of  which  many  are 
known  to  be  easily  oxidisable.  Pyrogallol  in  alkaline  solutions  greedily 
absorbs  oxygen  and  becomes  decomposed  into  carbonic  anhydride,  aCetic 
acid,  and  a  brown  body  ot'  unknown  nature.  The  dihydroxybenzenes 
(catechol,  resorcinol,  and  quinol)  are  easily  oxidisable  bodies,  and  their 
methyl  derivative  orcinol  is  colored  red  by  the  air.  As  regards  derivatives 
of  the  anthraquinone  series,  there  is  the  change  of  indigo-white  into  indigo- 
blue,  and  the  behavior  of  Boletus  luridus,  the  colorless  section  of  which 
becomes  at  once  blue  on  exposure  to  the  air.  Lastly,  there  is  a  series  of 
complex  plant-constituents,  undoubtedly  benzene  derivatives  although 
their  constitution  has  not  yet  been  ascertained,  which  exhibit  many  analo- 
gies to  the  discoloration  of  plant  juices.  Of  these  brazilin  may  be  named, 
the  colorless  aqueous  solution  of  which  becomes  first  yellowT,  then  reddish- 
yellow  in  the  air. 
The  author,  in  his  endeavors  to  isolate  the  easily  oxidisable  constituents 
of  the  sugar-beet  and  potato  to  which  the  discoloration  of  their  respective 
fluids  is  attributable,  succeeded  in  the  first  instance  in  isolating  from  the 
beet-root  a  chromogen  which  on  exposure  to  the  air  acquired  a  red  color. 
This  substance  he  has  accordingly  designated  Bhodogen.  The  product  of 
its  oxidation  he  terms  beet-red,  and  he  notes  certain  remarkable  analogies 
between  the  absorption-bands  of  this  substance  and  of  the  coloring  matter 
of  Anchusa  tinctoria,  alkanet  red,  the  spectrum  of  each  showing  three 
bands  occupying  identical  positions.  These  investigations  have  therefore 
so  far  afforded  proof  of  the  existence  in  the  colorless  cells  of  the  sugar-beet 
of  an  easily  oxidisable  colorless  body,  capable  of  isolation,  which  by  itself, 
without  the  aid  of  the  living  plasma  of  the  plant,  can  split  up  the  oxygen 
molecule,  forming  a  colored  substance. 
The  isolation  of  the  chromogen  of  the  potato  has  not  succeeded  so  satis- 
factorily. The  presence  of  vanillin  in  the  juice  appeared  to  be  shown  by 
the  strong  odor  of  vanilla.  Vanillin  has  been  detected  by  Scheibler  in  raw 
beet-sugar.  A  substance  resembling  catechol,  but  not  identical  with  it,  was 
also  separated.    It  would  seem  to  be  the  same  body  discovered  by  GForup- 
