﻿THE 
  ALG.E 
  

  

  231 
  

  

  growing 
  places. 
  This 
  is 
  true 
  in 
  the 
  case 
  of 
  Sargassum, 
  some 
  

   species 
  of 
  which 
  thrive 
  along 
  the 
  shores 
  of 
  tropical 
  oceans. 
  

   In 
  the 
  North 
  Atlantic 
  Ocean, 
  north 
  of 
  the 
  Canary 
  Islands, 
  

   is 
  a 
  body 
  of 
  water 
  known 
  as 
  the 
  Sargasso 
  Sea. 
  Its 
  entire 
  

   area 
  is 
  more 
  or 
  less 
  filled 
  with 
  floating 
  Sargasmm 
  and 
  other 
  

   forms 
  of 
  plant 
  and 
  animal 
  life. 
  Saryassum, 
  like 
  some 
  other 
  

   brown 
  algae, 
  is 
  peculiarly 
  fitted 
  

   for 
  floating 
  by 
  the 
  presence 
  

   of 
  " 
  air 
  bladders," 
  which 
  are 
  

   swollen 
  portions 
  of 
  the 
  leaf 
  -like 
  

   expansions 
  of 
  the 
  plant. 
  In 
  

   mid-ocean 
  one 
  may 
  see 
  small 
  

   floating 
  masses 
  of 
  these 
  plants, 
  

   which 
  have 
  been 
  carried 
  some- 
  

   times 
  hundreds 
  or 
  even 
  thou- 
  

   sands 
  of 
  miles 
  from 
  then.' 
  original 
  

   homes. 
  

  

  218. 
  The 
  kelps. 
  The 
  giant 
  

   kelps 
  belong 
  to 
  the 
  brown 
  algse. 
  

   The 
  cylindrical, 
  stem-like 
  plants 
  

   sometimes 
  (as 
  in 
  Macrocystisi) 
  

   reach 
  a 
  length 
  of 
  from 
  800 
  to 
  

   900 
  feet, 
  while 
  " 
  devil's 
  apron," 
  

   (Laminaria) 
  grows 
  into 
  strap- 
  

   like 
  or 
  widely 
  spread, 
  tough, 
  

   leathery 
  expansions. 
  All 
  of 
  

   these 
  forms 
  have 
  heavy, 
  root- 
  

   like 
  holdfasts, 
  which 
  are 
  so 
  strong 
  that 
  the 
  plant 
  will 
  usually 
  

   break 
  elsewhere 
  before 
  it 
  will 
  pull 
  away 
  from 
  its 
  support. 
  

  

  At 
  one 
  time 
  the 
  world's 
  supply 
  of 
  iodine 
  was 
  derived 
  from 
  

   the 
  brown 
  algte 
  ; 
  now 
  it 
  can 
  usually 
  be 
  prepared 
  more 
  eco- 
  

   nomically 
  by 
  chemical 
  means. 
  Soda 
  was 
  formerly 
  secured 
  

   from 
  these 
  plants, 
  but 
  chemical 
  processes 
  have 
  driven 
  out 
  the 
  

   laborious 
  methods 
  of 
  securing 
  that 
  substance 
  directly 
  from 
  

   plants. 
  Gelatinous 
  foods 
  and 
  a 
  sugar 
  known 
  as 
  mannite 
  are 
  

   secured 
  from 
  some 
  species 
  of 
  brown 
  algte. 
  In 
  some 
  coastal 
  

  

  FIG. 
  180. 
  Rockweed 
  (Fucus) 
  

  

  A, 
  the 
  base 
  of 
  a 
  young 
  plant, 
  showing 
  

   an 
  early 
  stage 
  in 
  formation 
  of 
  the 
  

   holdfast, 
  which 
  attached 
  the 
  plant 
  

   to 
  a 
  piece 
  of 
  wood. 
  B, 
  tip 
  of 
  a 
  plant 
  ; 
  

   b, 
  air 
  bladders; 
  a, 
  specialized 
  re- 
  

   gions 
  in 
  which 
  reproductive 
  organs 
  

   are 
  formed 
  ; 
  c, 
  new 
  leaf-like 
  growth 
  

   where 
  the 
  plant 
  has 
  been 
  broken. 
  

   A 
  little 
  less 
  than 
  natural 
  size 
  

  

  