ANTHOCYANINS  251

pound  has  a  red  tint.  When  treated  with  alkali,  blue  metallic
salts  are  formed,  while  the  arrangement  shown  in  the  formula
II.  represents  a  neutral  compound  having  a  violet  tint.  The
neutral  violet  tinted  delphinin  has  been  isolated  from  Del-
phinium consolida  by  Willstatter  and  Mieg,*  and  has  been
shown  to  turn  blue  with  alkali,  and  red  with  acids ;  the  colour
would  therefore  appear  to  act  as  an  indicator  in  the  plant
itself,  showing  whether  the  cell  sap  is  neutral  acid  or  alkaline.
CONNECTION  BETWEEN  ANTHOCYANINS  AND
ANTHOXANTHINS.
A  comparison  of  the  formula  of  cyanidin  chloride  on  page
250  with  that  of  quercetin  on  page  245  reveals  a  close  relation-
ship between  these  two  substances,  and  consequently  between
the  flavones  or  anthoxanthins  and  the  anthocyanins.  Theo-
retically it  should  be  possible  to  pass  from  anthoxanthins  to
anthocyanins  by  reduction,  or  conversely  from  anthocyanins
to  anthoxanthins  by  oxidation.  In  the  plant  no  doubt  this
is  effected  readily  enough  by  enzymes,  but  in  the  laboratory  it
is  more  difficult,  and  so  far  the  only  transformation  effected
has  been  the  reduction  of  quercetin  to  cyanidin.f  These  facts
provide  a  confirmation  of  the  views  put  forward  by  Wheldale
and  others  previous  to  this  definite  experimental  evidence.
Further  evidence  for  the  close  relationship  between  the  two
classes  of  compound  is  provided  by  the  fact  that  cyanidin  is
isomeric  with  luteolin  and  fisetin  while  delphinidin  is  isomeric
with  quercetin  and  morin.
EXTRACTION   OF   ANTHOCYANINS.
