In  this  way  Exogens  are  broken  up  into  2  groups,  the  one  Diclinous  and
the  other  Hermaphrodite.  The  latter  is  divided  by  almost  everybody
into  Polypetalous,  Monopetalous,  and  Apetalous  sub-classes  ;  following  the
old  systematists,  who  knew  of  little  beyond  external  characters,  and  had
small  acquaintance  with  any  plants  except  those  of  Europe.  But  all
experience  shows,  what  reason   seems  to  indicate,  that  no  great  natural


EXOGENS.  2-1 J

combinatioua  can  be  eflected  by  such  distinctions.  Exceptions  to  the
constancy  of  such  characters  are  endless  ;  there  is  probably  not  one  polype-
talous  Order  that  is  not  also  apetalous,  and  many  of  them  are  even
monopetalous,  of  which  Rueworts,  Ilouseleeks,  Anonads,  Leguminous  plants,
Milkworts,  and  many  more,  afford  famihar  examples.  The  apetalous  Orders
are  occasionally  polypetalous,  as  in  many  genera  of  Buckwheats  andDaphnads.
