﻿570 
  Setchell: 
  The 
  marine 
  spermatophytes 
  

  

  tropics 
  of 
  the 
  Red 
  Sea, 
  the 
  Indian 
  Ocean 
  and 
  the 
  tropical 
  portions 
  

   of 
  the 
  western 
  Pacific. 
  It 
  extends 
  also 
  around 
  Australia 
  and 
  to 
  

   the 
  northern 
  portion, 
  at 
  least, 
  of 
  Tasmania. 
  The 
  second 
  species 
  

   is 
  more 
  characteristic 
  of 
  the 
  northern 
  hemisphere, 
  extending 
  

   southward 
  from 
  the 
  arctic 
  regions 
  to 
  the 
  tropics 
  both 
  on 
  coasts 
  of 
  

   the 
  Atlantic 
  and 
  the 
  Pacific. 
  The 
  second 
  species, 
  however, 
  

   seems 
  to 
  be 
  rare 
  in 
  both 
  the 
  tropics 
  and 
  in 
  the 
  frigid 
  zones 
  and 
  

   probably 
  has' 
  its 
  center 
  of 
  distribution 
  in 
  one 
  or 
  other 
  of 
  the 
  

   intermediate 
  zones. 
  It 
  seems 
  best 
  to 
  examine 
  the 
  facts 
  concerning 
  

   both 
  of 
  these 
  species 
  in 
  some 
  detail. 
  

  

  The 
  first 
  species 
  of 
  this 
  really 
  extensive 
  distribution 
  to 
  be 
  con- 
  

   sidered 
  is 
  Halophila 
  ovalis 
  (R. 
  Br.) 
  Hook, 
  f., 
  which 
  is 
  generally 
  

   credited 
  with 
  being 
  widely 
  distributed 
  through 
  the 
  tropical 
  por- 
  

   tions 
  of 
  the 
  Red 
  Sea, 
  Indian 
  and 
  Pacific 
  Oceans. 
  It 
  also 
  extends 
  

   entirely 
  around 
  the 
  continent 
  of 
  Australia 
  and 
  occurs 
  on 
  the 
  

   shores 
  of 
  Tasmania 
  touched 
  by 
  Bass 
  Strait. 
  The 
  extensive 
  

   distribution 
  in 
  the 
  tropical 
  waters 
  seems 
  to 
  mark 
  this 
  species 
  as 
  

   normal 
  to 
  the 
  Tropical 
  Zone, 
  although 
  It 
  may 
  be 
  questioned 
  as 
  

   to 
  whether 
  one 
  or 
  more 
  species 
  are 
  included, 
  even 
  here, 
  under 
  the 
  

   name, 
  since 
  in 
  1909, 
  Ostenfeld 
  separated 
  the 
  plant 
  of 
  the 
  Marianne 
  

   and 
  Philippine 
  Islands 
  as 
  a 
  separate 
  species 
  under 
  the 
  name 
  of 
  

   Halophila 
  ovata 
  Gaud. 
  If 
  the 
  determinations 
  are 
  correct, 
  however 
  

   the 
  occurrence 
  of 
  H, 
  ovalis 
  on 
  the 
  coasts 
  of 
  Australia 
  extends 
  the 
  

   distribution 
  through 
  the 
  South 
  Subtropical 
  into 
  the 
  upper 
  portion 
  

   of 
  the 
  South 
  Temperate 
  Zone. 
  This 
  would 
  

  

  mean 
  

  

  of 
  temperatures 
  from 
  at 
  least 
  iS"" 
  or 
  19° 
  C. 
  upwards 
  to 
  about 
  

   ^29^ 
  C. 
  It 
  is 
  manifestly 
  impossible 
  to 
  do 
  more 
  than 
  to 
  discuss 
  a 
  

   case 
  like 
  this 
  and 
  to 
  suggest 
  possibilities 
  as 
  to 
  how 
  a 
  species, 
  whose 
  

  

  25° 
  

  

  may 
  t 
  

   mean 
  

  

  cated 
  as 
  about 
  iS"" 
  C. 
  or 
  at 
  most 
  19'* 
  C. 
  There 
  are, 
  however, 
  

   several 
  possibilities 
  which 
  might 
  be 
  investigated 
  by 
  those 
  having 
  - 
  

   an 
  opportunity 
  of 
  studying 
  the 
  living 
  plants. 
  In 
  the 
  first 
  place, 
  

   the 
  plants 
  of 
  the 
  Australian 
  and 
  Tasmanian 
  coasts 
  are 
  sterile, 
  or, 
  

   at 
  least, 
  have 
  not 
  been 
  found 
  in 
  other 
  than 
  vegetative 
  condition. 
  

   It 
  may 
  be 
  that 
  the 
  plants 
  of 
  these 
  countries 
  are 
  of 
  a 
  different 
  

   species 
  from 
  those 
  of 
  the 
  tropics. 
  In 
  opposition 
  to 
  this, 
  it 
  may 
  be 
  

   said 
  that 
  Ostenfeld 
  credits 
  this 
  species, 
  with 
  which 
  he 
  is 
  presum- 
  

  

  