﻿Setchell: 
  The 
  marhste 
  spermatophytes 
  575 
  

  

  slightly 
  different 
  temperature 
  relations, 
  the 
  narrow-leaved 
  forms 
  

   extending 
  farther 
  north 
  than 
  the 
  broader-leaved 
  forms; 
  

  

  (2) 
  all 
  forms 
  of 
  Zostera 
  marina 
  occupy 
  shallow 
  water 
  in 
  pro- 
  

   tected 
  bays 
  or 
  inlets 
  and, 
  consequently 
  inhabit 
  the 
  warmer 
  waters 
  

   of 
  the 
  zone 
  or 
  province 
  they 
  inhabit; 
  

  

  (3) 
  it 
  seems 
  most 
  probable 
  to 
  assume 
  that 
  the 
  North 
  Temper- 
  

   ate 
  Zone 
  is 
  the 
  normal 
  zone 
  for 
  Zostera 
  marina, 
  since 
  a 
  comparison 
  

   of 
  the 
  distribution 
  on 
  all 
  coasts 
  indicates 
  this 
  zone 
  rather 
  than 
  the 
  

   North 
  Subtropical 
  or 
  the 
  Lower 
  Boreal, 
  the 
  other 
  two 
  zones 
  in 
  

  

  which 
  it 
  is 
  widespread; 
  

  

  (4) 
  the 
  southward 
  invasion 
  from 
  the 
  North 
  Temperate 
  Zone 
  

   into 
  the 
  North 
  Subtropical 
  is 
  not 
  extensive 
  on 
  either 
  the 
  west 
  

   coast 
  of 
  Europe 
  or 
  on 
  the 
  west 
  coast 
  of 
  North 
  America, 
  but 
  is 
  

   extensive 
  on 
  the 
  east 
  coast 
  of 
  North 
  America 
  and 
  on 
  the 
  east 
  

   coast 
  of 
  Asia. 
  The 
  suggestion 
  naturally 
  is 
  that 
  these 
  latter 
  

   extensions 
  are 
  due 
  to 
  the 
  greater 
  deflections 
  of 
  the 
  colder 
  waters, 
  

   as 
  indicated 
  by 
  the 
  lines 
  of 
  mean 
  minima, 
  on 
  these 
  coasts, 
  i.e., 
  

   are 
  sea,sonal 
  invasions, 
  e.g., 
  chart 
  266 
  of 
  B. 
  M. 
  Davis 
  (1913, 
  

   p. 
  536) 
  indicates 
  that 
  Z. 
  marina 
  is 
  an 
  invader 
  from 
  colder 
  waters 
  

   at 
  Woods 
  Hole, 
  Massachusetts; 
  

  

  (5) 
  the 
  invasions 
  northward 
  from 
  the 
  North 
  Temperate 
  Zone 
  

   into 
  the 
  Boreal 
  Zones 
  are 
  probably 
  due 
  to 
  the 
  localities, 
  seemingly 
  

   always 
  situated 
  at 
  the 
  innermost 
  portions 
  of 
  long 
  fiords, 
  being 
  

   raised 
  in 
  temperature 
  (cf. 
  Kjellman, 
  1883, 
  p. 
  31) 
  by 
  the 
  air 
  tem- 
  

   perature 
  and 
  by 
  insolation; 
  

  

  (6) 
  it 
  may 
  also 
  be 
  urged 
  that 
  the 
  capacity 
  of 
  Zostera 
  marina 
  

   to 
  continue 
  its 
  occupation 
  of 
  a 
  particular 
  locality 
  and 
  to 
  spread 
  

   to 
  other 
  even 
  far 
  distant 
  localities, 
  through 
  its 
  adaptions 
  for 
  

   floating 
  and 
  vegetative 
  multiplication, 
  may 
  have 
  some 
  bearing 
  

   on 
  the 
  extensive 
  distribution 
  of 
  this 
  species 
  (cf. 
  Ascherson, 
  1906, 
  

  

  p. 
  402). 
  

  

  In 
  conclusion, 
  it 
  may 
  be 
  well 
  to 
  summarize 
  the 
  principal 
  

  

  points 
  of 
  general 
  interest 
  brought 
  out 
  or 
  suggested, 
  in 
  the 
  con- 
  

   sideration 
  of 
  the 
  marine 
  spermatophytes. 
  

  

  I. 
  The 
  marine 
  spermatophytes 
  are 
  largely 
  made 
  up 
  of 
  plants 
  

   surrounded 
  by 
  a 
  medium 
  whose 
  temperature 
  at 
  any 
  given 
  time 
  

   is 
  the 
  same 
  for 
  all 
  parts 
  of 
  the 
  plant. 
  The 
  species 
  of 
  Phyllospadix 
  

   alone 
  present 
  to 
  a 
  certain 
  extent, 
  at 
  least, 
  the 
  temperature 
  con- 
  

  

  