﻿Setchell: 
  The 
  marine 
  spermatophytes 
  571 
  

  

  able 
  familiar, 
  to 
  the 
  coast 
  of 
  Western 
  Australia 
  as 
  late 
  as 
  1916. 
  

   His 
  plants, 
  however, 
  were 
  sterile. 
  In 
  the 
  second 
  place, 
  this 
  matter 
  

   of 
  the 
  sterility 
  of 
  the 
  Australian 
  and 
  Tasmanian 
  specimens 
  which 
  

   seems 
  to 
  be 
  the 
  general 
  testimony 
  from 
  Bentham 
  in 
  1878 
  (vol. 
  7, 
  

   p. 
  183) 
  on 
  to 
  Ostenfeld 
  in 
  1916, 
  may 
  indicate 
  that 
  this 
  southern 
  

   extension 
  of 
  the 
  range 
  is 
  composed 
  of 
  plants 
  which 
  never 
  fruit 
  and 
  

   which 
  possibly 
  increase 
  in 
  number 
  and, 
  therefore 
  persist, 
  through 
  

   vegetative 
  multiplication 
  only. 
  Unfortunatelv, 
  there 
  is 
  too 
  little 
  

   information 
  as 
  the 
  habits 
  and 
  methods 
  of 
  dispersal 
  of 
  this 
  species, 
  

   but 
  it 
  is 
  extremely 
  likely 
  that 
  vegetative 
  methods 
  of 
  propagation 
  

   may 
  be 
  important 
  in 
  the 
  establishment 
  and 
  persistence 
  of 
  this 
  

   species. 
  The 
  third 
  and 
  possibly 
  the 
  most 
  probable 
  alternative 
  

   is 
  that 
  the 
  shallow 
  cooler 
  waters 
  inhabited 
  by 
  plants 
  of 
  this 
  species, 
  

   may 
  through 
  the 
  higher 
  temperature 
  of 
  the 
  air 
  and 
  through 
  insola- 
  

   tion 
  be 
  raised 
  six 
  or 
  eight 
  or 
  even 
  more 
  degrees 
  in 
  temperature 
  

   for 
  a 
  sufficient 
  number 
  of 
  days 
  or 
  weeks 
  to 
  enable 
  the 
  plants 
  to 
  

   flower 
  and 
  to 
  ripen 
  their 
  seeds. 
  This 
  amount 
  of 
  increase 
  of 
  the 
  

   temperature 
  of 
  shallow 
  protected 
  waters 
  is 
  known 
  to 
  occur. 
  While 
  

   no 
  one 
  of 
  these 
  three 
  possibilities 
  can 
  be 
  demonstrated 
  to 
  be 
  

   actually 
  in 
  operation, 
  yet 
  there 
  seems 
  to 
  be 
  sufficient 
  reason 
  for 
  not 
  

   regarding 
  the 
  extensive 
  distribution 
  of 
  this 
  species 
  as 
  indicating 
  a 
  

   eurythermal 
  character 
  so 
  far 
  as 
  persistence 
  through 
  seed-repro- 
  

  

  * 
  

  

  duction 
  Is 
  concerned. 
  That 
  the 
  species 
  in 
  general 
  is 
  eurythermal, 
  

  

  F 
  

  

  may 
  be 
  granted, 
  since 
  the 
  sum 
  total 
  of 
  its 
  endurance 
  extends 
  

   over 
  a 
  greater 
  interval 
  than 
  5^ 
  C. 
  or 
  even 
  10° 
  C. 
  We 
  may 
  suspect, 
  

   however 
  that 
  there 
  is 
  very 
  little 
  vital 
  activity 
  during 
  the 
  lower 
  

   periods 
  of 
  temperature 
  experienced, 
  but 
  the 
  ability 
  to 
  withstand 
  

   such 
  lower 
  temperatures 
  in 
  a 
  condition 
  of 
  quiescence 
  or 
  rigor. 
  

   In 
  other 
  words, 
  such 
  a 
  seeming 
  eurythermal 
  species 
  as 
  this 
  prob- 
  

   ably 
  is 
  able 
  to 
  endure 
  a 
  period 
  of 
  hibernation 
  while 
  the 
  other 
  

   strictly 
  tropical 
  species 
  of 
  Halopldla 
  are 
  not. 
  A 
  second 
  assump- 
  

   tion 
  in 
  the 
  case 
  of 
  Halophila 
  ovalis 
  is 
  that 
  it 
  is 
  a 
  perennial 
  species, 
  

   as 
  its 
  w^hole 
  appearance 
  and 
  general 
  structure 
  indicate. 
  

  

  The 
  second 
  and 
  other 
  species 
  of 
  marine 
  spermatophyte 
  credited 
  

   with 
  extensive 
  distribution 
  is 
  the 
  common 
  eel-grass 
  or 
  grass- 
  

   wrack, 
  Zostera 
  marina 
  L., 
  of 
  the 
  northern 
  hemisphere. 
  The 
  

   distribution 
  of 
  this 
  species, 
  as 
  generally 
  given, 
  extends 
  from 
  high 
  

   north 
  (at 
  least 
  Lower 
  Boreal 
  Zone) 
  to 
  well 
  within 
  the 
  Tropical 
  

  

  