﻿THE 
  SEED 
  PLANTS 
  305 
  

  

  changed 
  greatly 
  from 
  the 
  oldest 
  simple 
  plants. 
  While, 
  there- 
  

   fore, 
  we 
  compare 
  one 
  living 
  group 
  with 
  another, 
  we 
  must 
  keep 
  

   in 
  mind 
  the 
  fact 
  that 
  a 
  higher 
  group 
  of 
  living 
  plants 
  has 
  not 
  

   necessarily 
  developed 
  from 
  one 
  of 
  the 
  lower 
  living 
  groups, 
  

   but 
  rather 
  that 
  in 
  past 
  ages 
  a 
  common 
  ancestry 
  gave 
  rise 
  

   to 
  both. 
  The 
  lower 
  group 
  has 
  probably 
  changed 
  less 
  than 
  

   the 
  higher 
  one. 
  It 
  is 
  like 
  two 
  streams 
  of 
  water 
  that 
  have 
  

   their 
  source 
  on 
  the 
  top 
  of 
  the 
  same 
  mountain; 
  though 
  their 
  

   source 
  is 
  essentially 
  the 
  same, 
  the 
  conditions 
  under 
  which 
  

   they 
  flow 
  may 
  make 
  the 
  two 
  rivers 
  quite 
  unlike 
  when 
  they 
  

   reach 
  the 
  valleys 
  below. 
  

  

  290. 
  Brief 
  summary 
  of 
  the 
  groups. 
  1 
  The 
  thallophytes 
  con- 
  

   sist 
  of 
  simple 
  plants, 
  some 
  of 
  which 
  (the 
  algse) 
  possess 
  chloro- 
  

   phyll, 
  by 
  means 
  of 
  which 
  they 
  manufacture 
  their 
  own 
  foods. 
  

   Other 
  thallophytes 
  (the 
  fungi), 
  being 
  without 
  chlorophyll, 
  

   cannot 
  make 
  their 
  own 
  foods 
  and 
  are 
  dependent. 
  Depend- 
  

   ency 
  is 
  expressed 
  in 
  types 
  of 
  parasitism 
  and 
  saprophytism, 
  

   which 
  are 
  often 
  of 
  importance 
  to 
  other 
  living 
  things. 
  These 
  

   simple 
  plants 
  are 
  prostrate 
  and 
  are 
  not 
  differentiated 
  into 
  

   roots, 
  stems, 
  and 
  leaves. 
  While 
  reproduction 
  is 
  simple 
  in 
  

   this 
  first 
  group, 
  in 
  some 
  plants 
  we 
  find 
  specialized 
  sex 
  organs, 
  

   with 
  sperms 
  and 
  eggs 
  for 
  the 
  formation 
  of 
  sex- 
  spores. 
  

  

  In 
  the 
  bryophytes 
  the 
  moss 
  exhibits 
  a 
  much 
  more 
  complex 
  

   type 
  of 
  plant. 
  It 
  has 
  an 
  alga-like 
  stage 
  ; 
  then 
  it 
  sends 
  up 
  leafy 
  

   shoots, 
  which 
  expose 
  chlorophyll 
  to 
  the 
  light 
  in 
  a 
  better 
  way 
  

   than 
  appeared 
  in 
  the 
  thallophytes 
  ; 
  these 
  shoots 
  also 
  bear 
  

   highly 
  differentiated 
  sex 
  organs. 
  From 
  the 
  sex 
  spore 
  there 
  

   grows 
  a 
  special 
  asexual 
  spore-forming 
  stalk 
  and 
  capsule, 
  from 
  

  

  1 
  No 
  attempt 
  is 
  made 
  at 
  this 
  time 
  to 
  give 
  a 
  complete 
  summary 
  of 
  all 
  the 
  

   important 
  characters 
  of 
  the 
  groups 
  studied 
  ; 
  the 
  aim 
  has 
  been 
  rather 
  to 
  

   state 
  only 
  the 
  most 
  important 
  things 
  which 
  will 
  cause 
  each 
  group 
  to 
  stand 
  

   out 
  with 
  some 
  individuality 
  and 
  at 
  the 
  same 
  time 
  give 
  it 
  some 
  relation 
  to 
  the 
  

   series 
  of 
  groups 
  as 
  a 
  whole. 
  Neither 
  is 
  any 
  attempt 
  made 
  in 
  this 
  book 
  to 
  

   present 
  the 
  evolutionary 
  series 
  of 
  plants. 
  The 
  groups 
  are 
  presented 
  so 
  that 
  

   the 
  increasing 
  complexity 
  is 
  apparent, 
  but 
  the 
  close 
  evolutionary 
  connections 
  

   are 
  omitted, 
  and 
  the 
  emphasis 
  that 
  is 
  sometimes 
  placed 
  upon 
  evolution 
  is 
  

   here 
  placed 
  upon 
  securing 
  an 
  elementary 
  idea 
  of 
  the 
  kinds 
  of 
  common 
  plants 
  

   that 
  are 
  found 
  in 
  each 
  of 
  the 
  gre^t 
  groups, 
  

  

  