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  INTRODUCTION 
  TO 
  BOTANY 
  

  

  263. 
  Club-mosses, 
  or 
  ground 
  pines. 
  These 
  plants 
  constitute 
  

   another 
  class 
  of 
  the 
  pteridophytes. 
  The 
  most 
  common 
  ones 
  

   belong 
  to 
  the 
  genus 
  _/,//<///"/// 
  (iig. 
  218). 
  Lycopodium 
  

   plants 
  are 
  found 
  mostly 
  in 
  the 
  cooler 
  temperate 
  regions. 
  At 
  

   Christmas 
  time 
  they 
  are 
  shipped 
  and 
  used 
  extensively 
  in 
  deco- 
  

   ration 
  throughout 
  the 
  United 
  States. 
  Their 
  stems, 
  which 
  are 
  

   underground 
  or 
  under 
  leaves, 
  etc., 
  their 
  upright 
  branches 
  and 
  

   symmetrically 
  arranged 
  leaves, 
  and 
  their 
  prominent 
  spore- 
  

   bearing 
  cones 
  are 
  striking 
  features 
  of 
  these 
  plants. 
  The 
  col- 
  

   lections 
  of 
  sporophylls 
  in 
  these 
  plants 
  and 
  in 
  Uyuisetum 
  are 
  

   sometimes 
  spoken 
  of 
  as 
  flowers 
  but 
  are 
  more 
  properly 
  called 
  

   strobili, 
  or 
  cones. 
  

  

  264. 
  Pteridophytes 
  of 
  past 
  ages. 
  The 
  surface 
  of 
  the 
  earth 
  

   has 
  undergone 
  many 
  sweeping 
  changes 
  since 
  plants 
  first 
  began 
  

   to 
  live 
  upon 
  it. 
  In 
  some 
  periods 
  of 
  the 
  earth's 
  history 
  condi- 
  

   tions 
  favored 
  certain 
  kinds 
  of 
  plants, 
  and 
  these 
  flourished. 
  

   When 
  less 
  favorable 
  periods 
  came, 
  these 
  once-successful 
  plants 
  

   were 
  greatly 
  reduced 
  in 
  number, 
  or 
  possibly 
  were 
  eliminated. 
  

   We 
  have 
  records 
  of 
  what 
  some 
  of 
  these 
  former 
  plants 
  were. 
  

   These 
  records 
  were 
  made 
  by 
  the 
  plants 
  themselves, 
  for 
  when 
  

   they 
  died 
  they 
  sometimes 
  became 
  fossilized, 
  or 
  made 
  prints 
  in 
  

   soft 
  mud 
  or 
  other 
  substances 
  which 
  afterwards 
  hardened. 
  I'>y 
  

   means 
  of 
  fossils 
  much 
  is 
  being 
  learned 
  about 
  the 
  kinds 
  of 
  

   plants 
  that 
  used 
  to 
  exist. 
  The 
  ancient 
  fern-like 
  plants 
  were 
  

   widely 
  distributed 
  over 
  the 
  earth. 
  Certain 
  periods 
  (as 
  the 
  so- 
  

   called 
  carboniferous 
  period) 
  were 
  peculiarly 
  favorable 
  in 
  tem- 
  

   perature 
  and 
  moisture 
  to 
  the 
  growth 
  of 
  pteridophyte 
  types 
  of 
  

   plants, 
  and 
  they 
  grew 
  to 
  much 
  greater 
  size 
  and 
  in 
  much 
  greater 
  

   profusion 
  than 
  even 
  our 
  present 
  tree-ferns 
  of 
  the 
  moist 
  tropics. 
  

   After 
  a 
  long 
  period 
  of 
  growth, 
  when 
  multitudes 
  of 
  the 
  plants 
  

   had 
  died 
  and 
  fallen, 
  conditions 
  changed 
  and 
  these 
  masses 
  of 
  

   plant 
  material 
  became 
  submerged 
  and 
  then 
  buried 
  beneath 
  lay- 
  

   ers 
  of 
  rock 
  and 
  earth, 
  and 
  at 
  length 
  coal 
  was 
  formed 
  from 
  them. 
  

  

  265. 
  Classification. 
  The 
  following 
  classification 
  mayassistin 
  

   keeping 
  leading 
  facts 
  in 
  mind, 
  but 
  it 
  is 
  presented 
  as 
  a 
  means 
  

   of 
  review 
  rather 
  than 
  as 
  an 
  outline 
  to 
  be 
  committed 
  to 
  memory. 
  

  

  