That  fruit  pigeons  can  distribute  their  seeds  over  the  Pacific  has
been  long  established,  and  Mr.  Hemsley  includes  Psychotria
amongst  those  genera  which,  from  the  collections  of  fruits  and  seeds
found  in  the  crops  of  fruit-pigeons,  made  by  Professor  Moseley,
myself,  and  others,  in  the  groups  of  the  Western  Pacific,  are  "  known
to  be  dispersed  by  birds  in  Polynesia  "  {Introd.  BoL  ChalL  Exped,,
p.  45).  It  is  thus  hardly  necessary  to  point  out  that  neither  the
entire  fruits  nor  the  separate  pyrenes  could  be  transported  by  the
currents,  my  observations  showing  that  in  both  cases  they  sink  at
once  or  in  a  day  or  two.
Psychotria,  however,  is  an  enormous  genus  including,  according
to  the  Index  Kewensis,  some  600  or  700  described  species,  dis-
trfbuted  in  the  tropics  all  over  the  world,  and  also  extending  into-
subtropical  regions,  the  greatest  concentration  being  in  America.
It  is  described  in  the  Genera  Plantarum  as  a  polymorphous  genus
distinguished  by  no  certain  characters  from  some  other  genera  of


XXV  PSYCHOTRIA  315

the  tribe  of  the  Rubiaceae  to  which  it  has  given  its  name.  We  have
here  a  genus  that  has  overrun  the  tropical  regions  of  the  world,
probably  originating  in  America ;  and  we  may  contrast  it  with  the
relatively  small  Rubiaceous  genus  of  Coprosma  (with  its  three
score  of  species,  and  quite  comparable  with  it  from  the  stand-
point of  capacity  for  dispersal),  that,  having  its  birthplace  in  New
Zealand,  is  only  beginning  to  reach  the  mainlands  of  the  New  and
the  Old  World.
