﻿Setchell: 
  The 
  marine 
  spermatophytes 
  567 
  

  

  the 
  relation 
  either 
  to 
  isotherms 
  or 
  to 
  the 
  total 
  amount 
  of 
  heat 
  

   obtained 
  is 
  not 
  shown 
  with 
  any 
  exactness. 
  Ascherson, 
  also, 
  in 
  

   charting 
  the 
  distribution, 
  simply 
  draws 
  a 
  continuous 
  line 
  between 
  

   the 
  extreme 
  records 
  and 
  makes 
  an 
  enclosed 
  atea 
  as 
  if 
  of 
  continuous 
  

  

  * 
  

  

  occurrence 
  and 
  of 
  possibly 
  uniform 
  frequency. 
  The 
  results 
  are, 
  

   consequently, 
  confusing 
  and 
  misleading. 
  It 
  is, 
  nevertheless, 
  a 
  

   simple 
  matter 
  in 
  the 
  case 
  of 
  the 
  strictly 
  tropical 
  species. 
  They 
  

   are 
  in 
  the 
  great 
  majority 
  among 
  the 
  marine 
  spermatophytes 
  and 
  

   are 
  clearly 
  shown 
  as 
  inhabitants 
  of 
  the 
  warmer, 
  or 
  even 
  of 
  the 
  

   warmest 
  waters 
  of 
  the 
  oceans. 
  The 
  distribution 
  in 
  cases 
  of 
  the 
  

   smaller 
  number 
  of 
  inhabitants 
  of 
  the 
  temperate 
  zones, 
  as 
  these 
  

   are 
  understood 
  and 
  marked 
  off 
  on 
  the 
  ordinary 
  maps 
  seems 
  also 
  

   plain, 
  although 
  here 
  it 
  is 
  difficult 
  to 
  understand 
  in 
  the 
  case 
  of 
  

   certain 
  of 
  these 
  species 
  why 
  they 
  do 
  not 
  fill 
  out 
  their 
  "zones'* 
  

   more 
  completely. 
  One 
  species, 
  however, 
  shows 
  such 
  an 
  extensive 
  

   distribution 
  as 
  to 
  cause 
  special 
  remark 
  on 
  the 
  part 
  of 
  Ascherson. 
  

   This 
  is 
  the 
  common 
  '* 
  eel-grass'* 
  of 
  our 
  Atlantic 
  coast, 
  Zostera 
  

   marina. 
  As 
  plotted 
  by 
  Ascherson, 
  this 
  species 
  extends 
  from 
  the 
  

   Kara 
  Sea 
  (to 
  the 
  northwest 
  of 
  Asia) 
  down 
  to 
  Cadiz 
  in 
  Spain, 
  

   from 
  Iceland 
  to 
  Newfoundland 
  (avoiding 
  Greenland) 
  and 
  thence 
  

   down 
  the 
  eastern 
  coast 
  of 
  the 
  United 
  States 
  to 
  western 
  Florida, 
  

   from 
  Bering 
  Strait 
  to 
  and 
  including 
  Yakutat 
  Bay, 
  Alaska, 
  and 
  

   from 
  the 
  same 
  strait 
  down 
  along 
  the 
  east 
  coast 
  of 
  Asia 
  through 
  

   the 
  Loo 
  Choo 
  Islands 
  nearly, 
  but 
  not 
  quite, 
  to 
  Formosa. 
  Such 
  

   an 
  extensive 
  distribution 
  might 
  well 
  disturb 
  any 
  ideas 
  of 
  limits 
  of 
  

  

  distribution 
  at 
  all 
  narrow. 
  

  

  In 
  the 
  revised 
  reprint 
  of 
  his 
  paper, 
  issued 
  in 
  1906, 
  Ascherson 
  

   lists 
  thirty-two 
  species 
  of 
  marine 
  spermatophytes, 
  an 
  increase 
  of 
  

   ten 
  over 
  the 
  earher 
  issue, 
  some 
  of 
  which 
  had 
  resulted 
  from 
  segre- 
  

   gation 
  from 
  species 
  listed 
  before, 
  and 
  also 
  expresses 
  doubt 
  as 
  to 
  

   the 
  extreme 
  limits 
  of 
  the 
  distribution 
  of 
  Zostera 
  marina. 
  He 
  still 
  

   lays 
  stress, 
  however, 
  on 
  the 
  circles 
  and 
  the 
  tropics 
  in 
  their 
  relation 
  

   to 
  the 
  distribution 
  of 
  the 
  individual 
  species. 
  

  

  In 
  1907 
  Ascherson 
  contributed 
  the 
  accounts 
  of 
  the 
  marine 
  

   spermatophytes, 
  so 
  far 
  as 
  published, 
  to 
  the 
  **Pflanzenreich" 
  of 
  

   Engler, 
  and 
  Ostenfeld, 
  in 
  1902, 
  published 
  a 
  preliminary 
  revision 
  

   of 
  Halophila. 
  From 
  these, 
  as 
  well 
  as 
  from 
  other 
  sources, 
  it 
  seems 
  

   that 
  some 
  thirty-four 
  or 
  thirty-five 
  species 
  are 
  now 
  to 
  be 
  rccog- 
  

  

  