﻿THE 
  ALG.E 
  233 
  

  

  some 
  are 
  a 
  deep 
  purple. 
  Chlorophyll 
  is 
  present, 
  as 
  in 
  all 
  other 
  

   algte, 
  but 
  is 
  often 
  completely 
  obscured 
  by 
  the 
  other 
  colors. 
  

   Sometimes 
  all 
  the 
  colors 
  are 
  obscured 
  by 
  coatings 
  of 
  calcareous 
  

   material. 
  

  

  The 
  red 
  algfe 
  have 
  basal 
  holdfasts. 
  The 
  plants 
  are 
  exten- 
  

   sively 
  branched 
  (fig. 
  181) 
  and, 
  as 
  a 
  rule, 
  are 
  smaller 
  and 
  

   more 
  delicate 
  than 
  the 
  brown 
  forms. 
  1 
  The 
  entire 
  plant 
  often 
  

   looks 
  like 
  a 
  sparsely 
  branched 
  stem 
  with 
  many 
  finely 
  divided 
  

   leaves. 
  The 
  gelatinous 
  material 
  obtained 
  from 
  certain 
  of 
  the 
  

   red 
  algae 
  is 
  by 
  some 
  regarded 
  as 
  a 
  delicacy. 
  In 
  the 
  North 
  Sea 
  

   and 
  elsewhere 
  in 
  the 
  Atlantic 
  Ocean 
  occurs 
  a 
  red 
  alga 
  known 
  

   as 
  " 
  Irish 
  moss," 
  which 
  is 
  collected 
  in 
  large 
  quantities 
  and 
  

   employed 
  in 
  the 
  preparation 
  of 
  jelly, 
  to 
  be 
  used 
  both 
  directly 
  

   as 
  food 
  and 
  as 
  a 
  basis 
  for 
  the 
  preparation 
  of 
  other 
  foods. 
  

  

  PROBLEMS 
  

  

  1. 
  Why 
  are 
  the 
  blue-green 
  algae 
  on 
  the 
  whole 
  considered 
  to 
  be 
  of 
  

   lower 
  organization 
  than 
  the 
  green 
  algae 
  ? 
  

  

  2. 
  Which 
  of 
  these 
  groups 
  is 
  more 
  injurious 
  in 
  its 
  effect 
  on 
  reservoirs 
  

   of 
  drinking 
  water? 
  Why? 
  

  

  3. 
  Why 
  is 
  it 
  often 
  found 
  desirable 
  to 
  build 
  roofs 
  over 
  such 
  reservoirs? 
  

  

  4. 
  In 
  what 
  ways 
  do 
  algae 
  help 
  or 
  hinder 
  the 
  life 
  of 
  aquatic 
  animals? 
  

   How 
  does 
  an 
  aquarium 
  aid 
  in 
  answering 
  this 
  question? 
  What 
  bearing 
  

   on 
  it 
  has 
  the 
  fact 
  that 
  the 
  flinty 
  cell 
  coverings 
  of 
  some 
  of 
  the 
  micro- 
  

   scopic 
  algae 
  (diatoms) 
  are 
  found 
  in 
  the 
  digestive 
  cavities 
  of 
  oysters 
  ? 
  

  

  5. 
  What 
  algae 
  are 
  used 
  as 
  human 
  food? 
  

  

  6. 
  May 
  polishing 
  powders 
  or 
  pastes 
  be 
  made 
  of 
  fossil 
  remains 
  of 
  

   algae 
  ? 
  Use 
  a 
  compound 
  microscope 
  in 
  examining 
  some 
  such 
  powders. 
  

  

  7. 
  It 
  is 
  generally 
  supposed 
  that 
  algae 
  were 
  among 
  the 
  first 
  plants 
  

   to 
  appear 
  on 
  the 
  earth 
  in 
  very 
  early 
  geological 
  times. 
  Does 
  this 
  seem 
  

   probable 
  ? 
  

  

  8. 
  How 
  do 
  the 
  algae 
  pass 
  through 
  the 
  winter 
  and 
  seasons 
  of 
  drought? 
  

  

  1 
  The 
  best 
  way 
  for 
  the 
  teacher 
  to 
  give 
  a 
  general 
  notion 
  of 
  brown 
  and 
  red 
  

   algae 
  is 
  to 
  secure 
  card 
  mounts 
  or 
  bottled 
  material 
  for 
  class 
  demonstrations 
  

   of 
  a 
  few 
  of 
  the 
  leading 
  types 
  in 
  each 
  group. 
  These 
  may 
  be 
  obtained 
  from 
  

   the 
  Woods 
  Hole 
  Biological 
  Laboratory, 
  Woods 
  Hole, 
  Massachusetts, 
  and 
  

   from 
  other 
  reliable 
  supply 
  houses. 
  Well-prepared 
  card 
  mounts 
  preserve 
  

   the 
  natural 
  colors, 
  and 
  may 
  be 
  kept 
  indefinitely 
  for 
  laboratory 
  use. 
  

  

  