ToVeXe'rPm3m'}       Distribution  of  Tannin  Plants.  519 
the  results  of  his  own  extensive  researches  are  so  combined  with 
those  recorded  in  the  widely  distributed  literature  of  the  tannins  that 
the  whole  presents  a  mass  of  data  from  which  important  generaliza- 
tions may  be  made.  However,  since  the  number  of  plants  in  which 
the  presence  or  absence  of  tannin  has  been  determined  is  relatively 
small  in  comparison  with  the  number  of  known  species  of  plants,  it 
is  very  probable  that  these  generalizations  will  be  more  or  less  modi- 
fied by  future  investigations. 
When  the  groups  or  subdivisions  into  which  botanists  divide 
the  plant  kingdom  are  considered  with  respect  to  the  occurrence  of 
tannin  therein  it  appears  that  some  forms  of  this  compound  appear 
in  all  of  the  main  groups  of  plants,  but  that  in  every  group  there 
are  many  families  that -contain  little  or  no  tannin.  In  the  lower 
groups  of  plants  represented  by  the  algae,  fungi  and  lichens,  tannin 
is  of  frequent  occurrence  but  owing  to  the  relatively  small  mass  of 
plant  material  furnished  by  these  groups  the  total  quantity  of  tannin 
produced  is  not  sufficient  to  have  any  commercial  importance.  In 
the  next  group,  the  mosses,  very  few  plants  have  been  found  which 
give  a  positive  reaction  for  tannin.  The  group  which  includes  the 
ferns  has  numerous  species  which  vary  in  tannin  content  from  a 
mere  trace  to  as  much  as  10  per  cent.,  but  it  is  in  the  higher  group  of 
seed-plants  that  tannin  occurs  most  abundantly. 
The  subdivision  of  seed-plants,  known  as  the  Gymnosperms, 
contains  a  large  number  of  plants  which  have  a  high  tannin  content. 
The  most  important  of  these  are  species  of  trees  such  as  the  pine, 
hemlock,  spruce  and  fir.  On  the  other  hand  among  the  Monocoty- 
ledons the  number  of  families  in  which  tannin  has  been  found  is 
small,  and  of  these  the  Palmse  is  the  only  one  in  which  there  are 
plants  which  furnish  tannin  in  commercial  quantity.  Among  the 
hundreds  of  species  of  the  families  which  include  the  grasses,  sedges 
and  lilies,  the  occurrence  of  tannin  even  in  very  small  quantities  is 
quite  rare. 
The  last  and  most  important  division  of  the  seed-plants,  the 
Dicotyledons,  furnish  by  far  the  largest  number  of  plants  rich  in 
tannin.  The  respective  natural  orders  comprising  the  Dicotyledons 
vary  greatly,  as  has  been  pointed  out  by  Dr.  Dekker,  in  respect  to  the 
manner  in  which  tannin  is  distributed  among  the  various  families. 
In  every  order  it  frequently  occurs  that  of  two  closely  related  families 
the  plants  of  one  will  be  rich  in  tannin  while  in  the  plants  of  the 
other,  tannin  will  occur  either  in  very  small  quantities  or  not  at  all. 
